How to get RSACryptoServiceProvider public and private key only in c#

0

I am running below code to get public and private key only, but it seems it outputs the whole XML format. I only need to output the keys as shown in Public and Private Key demo

        static RSACryptoServiceProvider rsa;

        private RSAParameters _privateKey;

        private RSAParameters _publicKey;

        public RSACrypto()

        {

            rsa = new RSACryptoServiceProvider(2048);

            _privateKey = rsa.ExportParameters(true);

            _publicKey = rsa.ExportParameters(false);



        }

        public string GetPublicKeyString()

        {

            var sw = new StringWriter();

            var xs = new XmlSerializer(typeof(RSAParameters));

            xs.Serialize(sw, _publicKey);

            return sw.ToString();

        }

        public string GetPrivateKeyString()

        {

            var sw = new StringWriter();

            var xs = new XmlSerializer(typeof(RSAParameters));

            xs.Serialize(sw, _privateKey);

            return sw.ToString();

        }

c# asp.net rsa public-key-encryption

share|improve this question

asked Jan 1 at 18:28

ARHARH

5332932

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  See the second answer of this question. stackoverflow.com/questions/14047532/…
  
  – NthDeveloper
  Jan 1 at 20:47
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @NthDeveloper: That answer has nothing to do with this question.
  
  – James K Polk
  Jan 1 at 21:49
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You can use the Bouncycastle C# library which is the easiest solution or you can try to hand code the generation of ASN.1 objects yourself which is doable but much harder.
  
  – James K Polk
  Jan 1 at 21:52
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In .NET Core 3.0 (preview 1) you can get the binary data with rsa.ExportSubjectPublicKeyInfo() and rsa.ExportRSAPrivateKey(), I’ll post an answer tomorrow.
  
  – bartonjs
  Jan 2 at 3:49
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @JamesKPolk thank you, I used BouncyCastle C# library, please write it as an answer to close this thread.
  
  – ARH
  Jan 2 at 10:48
  

  
  
  
  

add a comment | 

0

I am running below code to get public and private key only, but it seems it outputs the whole XML format. I only need to output the keys as shown in Public and Private Key demo

        static RSACryptoServiceProvider rsa;

        private RSAParameters _privateKey;

        private RSAParameters _publicKey;

        public RSACrypto()

        {

            rsa = new RSACryptoServiceProvider(2048);

            _privateKey = rsa.ExportParameters(true);

            _publicKey = rsa.ExportParameters(false);



        }

        public string GetPublicKeyString()

        {

            var sw = new StringWriter();

            var xs = new XmlSerializer(typeof(RSAParameters));

            xs.Serialize(sw, _publicKey);

            return sw.ToString();

        }

        public string GetPrivateKeyString()

        {

            var sw = new StringWriter();

            var xs = new XmlSerializer(typeof(RSAParameters));

            xs.Serialize(sw, _privateKey);

            return sw.ToString();

        }

c# asp.net rsa public-key-encryption

share|improve this question

asked Jan 1 at 18:28

ARHARH

5332932

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  See the second answer of this question. stackoverflow.com/questions/14047532/…
  
  – NthDeveloper
  Jan 1 at 20:47
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @NthDeveloper: That answer has nothing to do with this question.
  
  – James K Polk
  Jan 1 at 21:49
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You can use the Bouncycastle C# library which is the easiest solution or you can try to hand code the generation of ASN.1 objects yourself which is doable but much harder.
  
  – James K Polk
  Jan 1 at 21:52
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In .NET Core 3.0 (preview 1) you can get the binary data with rsa.ExportSubjectPublicKeyInfo() and rsa.ExportRSAPrivateKey(), I’ll post an answer tomorrow.
  
  – bartonjs
  Jan 2 at 3:49
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @JamesKPolk thank you, I used BouncyCastle C# library, please write it as an answer to close this thread.
  
  – ARH
  Jan 2 at 10:48
  

  
  
  
  

add a comment | 

0

0

0

I am running below code to get public and private key only, but it seems it outputs the whole XML format. I only need to output the keys as shown in Public and Private Key demo

        static RSACryptoServiceProvider rsa;

        private RSAParameters _privateKey;

        private RSAParameters _publicKey;

        public RSACrypto()

        {

            rsa = new RSACryptoServiceProvider(2048);

            _privateKey = rsa.ExportParameters(true);

            _publicKey = rsa.ExportParameters(false);



        }

        public string GetPublicKeyString()

        {

            var sw = new StringWriter();

            var xs = new XmlSerializer(typeof(RSAParameters));

            xs.Serialize(sw, _publicKey);

            return sw.ToString();

        }

        public string GetPrivateKeyString()

        {

            var sw = new StringWriter();

            var xs = new XmlSerializer(typeof(RSAParameters));

            xs.Serialize(sw, _privateKey);

            return sw.ToString();

        }

c# asp.net rsa public-key-encryption

share|improve this question

asked Jan 1 at 18:28

ARHARH

5332932

I am running below code to get public and private key only, but it seems it outputs the whole XML format. I only need to output the keys as shown in Public and Private Key demo

        static RSACryptoServiceProvider rsa;

        private RSAParameters _privateKey;

        private RSAParameters _publicKey;

        public RSACrypto()

        {

            rsa = new RSACryptoServiceProvider(2048);

            _privateKey = rsa.ExportParameters(true);

            _publicKey = rsa.ExportParameters(false);



        }

        public string GetPublicKeyString()

        {

            var sw = new StringWriter();

            var xs = new XmlSerializer(typeof(RSAParameters));

            xs.Serialize(sw, _publicKey);

            return sw.ToString();

        }

        public string GetPrivateKeyString()

        {

            var sw = new StringWriter();

            var xs = new XmlSerializer(typeof(RSAParameters));

            xs.Serialize(sw, _privateKey);

            return sw.ToString();

        }

c# asp.net rsa public-key-encryption

c# asp.net rsa public-key-encryption

share|improve this question

asked Jan 1 at 18:28

ARHARH

5332932

share|improve this question

asked Jan 1 at 18:28

ARHARH

5332932

share|improve this question

share|improve this question

asked Jan 1 at 18:28

ARHARH

5332932

asked Jan 1 at 18:28

ARHARH

5332932

asked Jan 1 at 18:28

ARHARH

5332932

5332932

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  See the second answer of this question. stackoverflow.com/questions/14047532/…
  
  – NthDeveloper
  Jan 1 at 20:47
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @NthDeveloper: That answer has nothing to do with this question.
  
  – James K Polk
  Jan 1 at 21:49
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You can use the Bouncycastle C# library which is the easiest solution or you can try to hand code the generation of ASN.1 objects yourself which is doable but much harder.
  
  – James K Polk
  Jan 1 at 21:52
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In .NET Core 3.0 (preview 1) you can get the binary data with rsa.ExportSubjectPublicKeyInfo() and rsa.ExportRSAPrivateKey(), I’ll post an answer tomorrow.
  
  – bartonjs
  Jan 2 at 3:49
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @JamesKPolk thank you, I used BouncyCastle C# library, please write it as an answer to close this thread.
  
  – ARH
  Jan 2 at 10:48
  

  
  
  
  

add a comment | 

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  See the second answer of this question. stackoverflow.com/questions/14047532/…
  
  – NthDeveloper
  Jan 1 at 20:47
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @NthDeveloper: That answer has nothing to do with this question.
  
  – James K Polk
  Jan 1 at 21:49
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  You can use the Bouncycastle C# library which is the easiest solution or you can try to hand code the generation of ASN.1 objects yourself which is doable but much harder.
  
  – James K Polk
  Jan 1 at 21:52
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In .NET Core 3.0 (preview 1) you can get the binary data with rsa.ExportSubjectPublicKeyInfo() and rsa.ExportRSAPrivateKey(), I’ll post an answer tomorrow.
  
  – bartonjs
  Jan 2 at 3:49
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @JamesKPolk thank you, I used BouncyCastle C# library, please write it as an answer to close this thread.
  
  – ARH
  Jan 2 at 10:48
  

  
  
  
  

See the second answer of this question. stackoverflow.com/questions/14047532/…

– NthDeveloper
Jan 1 at 20:47

See the second answer of this question. stackoverflow.com/questions/14047532/…

– NthDeveloper
Jan 1 at 20:47

@NthDeveloper: That answer has nothing to do with this question.

– James K Polk
Jan 1 at 21:49

@NthDeveloper: That answer has nothing to do with this question.

– James K Polk
Jan 1 at 21:49

1

1

You can use the Bouncycastle C# library which is the easiest solution or you can try to hand code the generation of ASN.1 objects yourself which is doable but much harder.

– James K Polk
Jan 1 at 21:52

You can use the Bouncycastle C# library which is the easiest solution or you can try to hand code the generation of ASN.1 objects yourself which is doable but much harder.

– James K Polk
Jan 1 at 21:52

In .NET Core 3.0 (preview 1) you can get the binary data with rsa.ExportSubjectPublicKeyInfo() and rsa.ExportRSAPrivateKey(), I’ll post an answer tomorrow.

– bartonjs
Jan 2 at 3:49

In .NET Core 3.0 (preview 1) you can get the binary data with rsa.ExportSubjectPublicKeyInfo() and rsa.ExportRSAPrivateKey(), I’ll post an answer tomorrow.

– bartonjs
Jan 2 at 3:49

@JamesKPolk thank you, I used BouncyCastle C# library, please write it as an answer to close this thread.

– ARH
Jan 2 at 10:48

@JamesKPolk thank you, I used BouncyCastle C# library, please write it as an answer to close this thread.

– ARH
Jan 2 at 10:48

add a comment | 

2 Answers
2

active

oldest

votes

0

The Bouncycastle C# library has some helper classes that can make this relatively easy. It is not well documented unfortunately. Here is an example:

using System;

using System.IO;

using System.Security.Cryptography;

using Org.BouncyCastle.OpenSsl;

using Org.BouncyCastle.Security;



namespace ExportToStandardFormats

{

    class MainClass

    {



        public static void Main(string args)

        {

            var rsa = new RSACryptoServiceProvider(2048);

            var rsaKeyPair = DotNetUtilities.GetRsaKeyPair(rsa);

            var writer = new StringWriter();

            var pemWriter = new PemWriter(writer);

            pemWriter.WriteObject(rsaKeyPair.Public);

            pemWriter.WriteObject(rsaKeyPair.Private);

            Console.WriteLine(writer);

        }

    }

}

share|improve this answer

answered Jan 2 at 19:27

James K PolkJames K Polk

30.3k116897

add a comment | 

1

Starting in .NET Core 3.0, this is (largely) built-in.

Writing SubjectPublicKeyInfo and RSAPrivateKey

.NET Core 3.0 built-in API

The output of the builtin API is the binary representation, to make them PEM you need to output the header, footer, and base64:

private static string MakePem(byte ber, string header)

{

    StringBuilder builder = new StringBuilder("-----BEGIN ");

    builder.Append(header);

    builder.AppendLine("-----");



    string base64 = Convert.ToBase64String(ber);

    int offset = 0;

    const int LineLength = 64;



    while (offset < base64.Length)

    {

        int lineEnd = Math.Min(offset + LineLength, base64.Length);

        builder.AppendLine(base64.Substring(offset, lineEnd - offset));

        offset = lineEnd;

    }



    builder.Append("-----END ");

    builder.Append(header);

    builder.AppendLine("-----");

    return builder.ToString();

}

So to produce the strings:

string publicKey = MakePem(rsa.ExportSubjectPublicKeyInfo(), "PUBLIC KEY");

string privateKey = MakePem(rsa.ExportRSAPrivateKey(), "RSA PRIVATE KEY");

Semi-manually

If you can't use .NET Core 3.0, but you can use pre-release NuGet packages, you can make use of the prototype ASN.1 writer package (which is the same code that's used internally in .NET Core 3.0; it's just that the API surface isn't finalized).

To make the public key:

private static string ToSubjectPublicKeyInfo(RSA rsa)

{

    RSAParameters rsaParameters = rsa.ExportParameters(false);



    AsnWriter writer = new AsnWriter(AsnEncodingRules.DER);

    writer.PushSequence();



    writer.PushSequence();

    writer.WriteObjectIdentifier("1.2.840.113549.1.1.1");

    writer.WriteNull();

    writer.PopSequence();



    AsnWriter innerWriter = new AsnWriter(AsnEncodingRules.DER);



    innerWriter.PushSequence();

    WriteRSAParameter(innerWriter, rsaParameters.Modulus);

    WriteRSAParameter(innerWriter, rsaParameters.Exponent);

    innerWriter.PopSequence();



    writer.WriteBitString(innerWriter.Encode());



    writer.PopSequence();

    return MakePem(writer.Encode(), "PUBLIC KEY");

}

And to make the private key:

private static string ToRSAPrivateKey(RSA rsa)

{

    RSAParameters rsaParameters = rsa.ExportParameters(true);



    AsnWriter writer = new AsnWriter(AsnEncodingRules.DER);

    writer.PushSequence();



    writer.WriteInteger(0);

    WriteRSAParameter(writer, rsaParameters.Modulus);

    WriteRSAParameter(writer, rsaParameters.Exponent);

    WriteRSAParameter(writer, rsaParameters.D);

    WriteRSAParameter(writer, rsaParameters.P);

    WriteRSAParameter(writer, rsaParameters.Q);

    WriteRSAParameter(writer, rsaParameters.DP);

    WriteRSAParameter(writer, rsaParameters.DQ);

    WriteRSAParameter(writer, rsaParameters.InverseQ);



    writer.PopSequence();

    return MakePem(writer.Encode(), "RSA PRIVATE KEY");

}

Reading them back

.NET Core 3.0 built-in API

Except that .NET Core 3.0 doesn't understand PEM encoding, so you have to do PEM->binary yourself:

private const string RsaPrivateKey = "RSA PRIVATE KEY";

private const string SubjectPublicKeyInfo = "PUBLIC KEY";



private static byte PemToBer(string pem, string header)

{

    // Technically these should include a newline at the end,

    // and either newline-or-beginning-of-data at the beginning.

    string begin = $"-----BEGIN {header}-----";

    string end = $"-----END {header}-----";



    int beginIdx = pem.IndexOf(begin);

    int base64Start = beginIdx + begin.Length;

    int endIdx = pem.IndexOf(end, base64Start);



    return Convert.FromBase64String(pem.Substring(base64Start, endIdx - base64Start));

}

Once that's done you can now load the keys:

using (RSA rsa = RSA.Create())

{

    rsa.ImportRSAPrivateKey(PemToBer(pemPrivateKey, RsaPrivateKey), out _);



    ...

}



using (RSA rsa = RSA.Create())

{

    rsa.ImportSubjectPublicKeyInfo(PemToBer(pemPublicKey, SubjectPublicKeyInfo), out _);



    ...

}

Semi-manually

If you can't use .NET Core 3.0, but you can use pre-release NuGet packages, you can make use of the prototype ASN.1 reader package (which is the same code that's used internally in .NET Core 3.0; it's just that the API surface isn't finalized).

For the public key:

private static RSA FromSubjectPublicKeyInfo(string pem)

{

    AsnReader reader = new AsnReader(PemToBer(pem, SubjectPublicKeyInfo), AsnEncodingRules.DER);

    AsnReader spki = reader.ReadSequence();

    reader.ThrowIfNotEmpty();



    AsnReader algorithmId = spki.ReadSequence();



    if (algorithmId.ReadObjectIdentifierAsString() != "1.2.840.113549.1.1.1")

    {

        throw new InvalidOperationException();

    }



    algorithmId.ReadNull();

    algorithmId.ThrowIfNotEmpty();



    AsnReader rsaPublicKey = spki.ReadSequence();



    RSAParameters rsaParameters = new RSAParameters

    {

        Modulus = ReadNormalizedInteger(rsaPublicKey),

        Exponent = ReadNormalizedInteger(rsaPublicKey),

    };



    rsaPublicKey.ThrowIfNotEmpty();



    RSA rsa = RSA.Create();

    rsa.ImportParameters(rsaParameters);

    return rsa;

}



private static byte ReadNormalizedInteger(AsnReader reader)

{

    ReadOnlyMemory<byte> memory = reader.ReadIntegerBytes();

    ReadOnlySpan<byte> span = memory.Span;



    if (span[0] == 0)

    {

        span = span.Slice(1);

    }



    return span.ToArray();

}

And because the private key values have to have the correct size arrays, the private key one is just a little trickier:

private static RSA FromRSAPrivateKey(string pem)

{

    AsnReader reader = new AsnReader(PemToBer(pem, RsaPrivateKey), AsnEncodingRules.DER);

    AsnReader rsaPrivateKey = reader.ReadSequence();

    reader.ThrowIfNotEmpty();



    if (!rsaPrivateKey.TryReadInt32(out int version) || version != 0)

    {

        throw new InvalidOperationException();

    }



    byte modulus = ReadNormalizedInteger(rsaPrivateKey);

    int halfModulusLen = (modulus.Length + 1) / 2;



    RSAParameters rsaParameters = new RSAParameters

    {

        Modulus = modulus,

        Exponent = ReadNormalizedInteger(rsaPrivateKey),

        D = ReadNormalizedInteger(rsaPrivateKey, modulus.Length),

        P = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        Q = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        DP = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        DQ = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        InverseQ = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

    };



    rsaPrivateKey.ThrowIfNotEmpty();



    RSA rsa = RSA.Create();

    rsa.ImportParameters(rsaParameters);

    return rsa;

}



private static byte ReadNormalizedInteger(AsnReader reader, int length)

{

    ReadOnlyMemory<byte> memory = reader.ReadIntegerBytes();

    ReadOnlySpan<byte> span = memory.Span;



    if (span[0] == 0)

    {

        span = span.Slice(1);

    }



    byte buf = new byte[length];

    int skipSize = length - span.Length;

    span.CopyTo(buf.AsSpan(skipSize));

    return buf;

}

share|improve this answer

edited Jan 2 at 18:57

answered Jan 2 at 18:14

bartonjsbartonjs

13.9k12658

add a comment | 

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

active

oldest

votes

active

oldest

votes

0

The Bouncycastle C# library has some helper classes that can make this relatively easy. It is not well documented unfortunately. Here is an example:

using System;

using System.IO;

using System.Security.Cryptography;

using Org.BouncyCastle.OpenSsl;

using Org.BouncyCastle.Security;



namespace ExportToStandardFormats

{

    class MainClass

    {



        public static void Main(string args)

        {

            var rsa = new RSACryptoServiceProvider(2048);

            var rsaKeyPair = DotNetUtilities.GetRsaKeyPair(rsa);

            var writer = new StringWriter();

            var pemWriter = new PemWriter(writer);

            pemWriter.WriteObject(rsaKeyPair.Public);

            pemWriter.WriteObject(rsaKeyPair.Private);

            Console.WriteLine(writer);

        }

    }

}

share|improve this answer

answered Jan 2 at 19:27

James K PolkJames K Polk

30.3k116897

add a comment | 

0

The Bouncycastle C# library has some helper classes that can make this relatively easy. It is not well documented unfortunately. Here is an example:

using System;

using System.IO;

using System.Security.Cryptography;

using Org.BouncyCastle.OpenSsl;

using Org.BouncyCastle.Security;



namespace ExportToStandardFormats

{

    class MainClass

    {



        public static void Main(string args)

        {

            var rsa = new RSACryptoServiceProvider(2048);

            var rsaKeyPair = DotNetUtilities.GetRsaKeyPair(rsa);

            var writer = new StringWriter();

            var pemWriter = new PemWriter(writer);

            pemWriter.WriteObject(rsaKeyPair.Public);

            pemWriter.WriteObject(rsaKeyPair.Private);

            Console.WriteLine(writer);

        }

    }

}

share|improve this answer

answered Jan 2 at 19:27

James K PolkJames K Polk

30.3k116897

add a comment | 

0

0

0

The Bouncycastle C# library has some helper classes that can make this relatively easy. It is not well documented unfortunately. Here is an example:

using System;

using System.IO;

using System.Security.Cryptography;

using Org.BouncyCastle.OpenSsl;

using Org.BouncyCastle.Security;



namespace ExportToStandardFormats

{

    class MainClass

    {



        public static void Main(string args)

        {

            var rsa = new RSACryptoServiceProvider(2048);

            var rsaKeyPair = DotNetUtilities.GetRsaKeyPair(rsa);

            var writer = new StringWriter();

            var pemWriter = new PemWriter(writer);

            pemWriter.WriteObject(rsaKeyPair.Public);

            pemWriter.WriteObject(rsaKeyPair.Private);

            Console.WriteLine(writer);

        }

    }

}

share|improve this answer

answered Jan 2 at 19:27

James K PolkJames K Polk

30.3k116897

The Bouncycastle C# library has some helper classes that can make this relatively easy. It is not well documented unfortunately. Here is an example:

using System;

using System.IO;

using System.Security.Cryptography;

using Org.BouncyCastle.OpenSsl;

using Org.BouncyCastle.Security;



namespace ExportToStandardFormats

{

    class MainClass

    {



        public static void Main(string args)

        {

            var rsa = new RSACryptoServiceProvider(2048);

            var rsaKeyPair = DotNetUtilities.GetRsaKeyPair(rsa);

            var writer = new StringWriter();

            var pemWriter = new PemWriter(writer);

            pemWriter.WriteObject(rsaKeyPair.Public);

            pemWriter.WriteObject(rsaKeyPair.Private);

            Console.WriteLine(writer);

        }

    }

}

share|improve this answer

answered Jan 2 at 19:27

James K PolkJames K Polk

30.3k116897

share|improve this answer

share|improve this answer

answered Jan 2 at 19:27

James K PolkJames K Polk

30.3k116897

answered Jan 2 at 19:27

James K PolkJames K Polk

30.3k116897

answered Jan 2 at 19:27

James K PolkJames K Polk

30.3k116897

30.3k116897

add a comment | 

add a comment | 

1

Starting in .NET Core 3.0, this is (largely) built-in.

Writing SubjectPublicKeyInfo and RSAPrivateKey

.NET Core 3.0 built-in API

The output of the builtin API is the binary representation, to make them PEM you need to output the header, footer, and base64:

private static string MakePem(byte ber, string header)

{

    StringBuilder builder = new StringBuilder("-----BEGIN ");

    builder.Append(header);

    builder.AppendLine("-----");



    string base64 = Convert.ToBase64String(ber);

    int offset = 0;

    const int LineLength = 64;



    while (offset < base64.Length)

    {

        int lineEnd = Math.Min(offset + LineLength, base64.Length);

        builder.AppendLine(base64.Substring(offset, lineEnd - offset));

        offset = lineEnd;

    }



    builder.Append("-----END ");

    builder.Append(header);

    builder.AppendLine("-----");

    return builder.ToString();

}

So to produce the strings:

string publicKey = MakePem(rsa.ExportSubjectPublicKeyInfo(), "PUBLIC KEY");

string privateKey = MakePem(rsa.ExportRSAPrivateKey(), "RSA PRIVATE KEY");

Semi-manually

If you can't use .NET Core 3.0, but you can use pre-release NuGet packages, you can make use of the prototype ASN.1 writer package (which is the same code that's used internally in .NET Core 3.0; it's just that the API surface isn't finalized).

To make the public key:

private static string ToSubjectPublicKeyInfo(RSA rsa)

{

    RSAParameters rsaParameters = rsa.ExportParameters(false);



    AsnWriter writer = new AsnWriter(AsnEncodingRules.DER);

    writer.PushSequence();



    writer.PushSequence();

    writer.WriteObjectIdentifier("1.2.840.113549.1.1.1");

    writer.WriteNull();

    writer.PopSequence();



    AsnWriter innerWriter = new AsnWriter(AsnEncodingRules.DER);



    innerWriter.PushSequence();

    WriteRSAParameter(innerWriter, rsaParameters.Modulus);

    WriteRSAParameter(innerWriter, rsaParameters.Exponent);

    innerWriter.PopSequence();



    writer.WriteBitString(innerWriter.Encode());



    writer.PopSequence();

    return MakePem(writer.Encode(), "PUBLIC KEY");

}

And to make the private key:

private static string ToRSAPrivateKey(RSA rsa)

{

    RSAParameters rsaParameters = rsa.ExportParameters(true);



    AsnWriter writer = new AsnWriter(AsnEncodingRules.DER);

    writer.PushSequence();



    writer.WriteInteger(0);

    WriteRSAParameter(writer, rsaParameters.Modulus);

    WriteRSAParameter(writer, rsaParameters.Exponent);

    WriteRSAParameter(writer, rsaParameters.D);

    WriteRSAParameter(writer, rsaParameters.P);

    WriteRSAParameter(writer, rsaParameters.Q);

    WriteRSAParameter(writer, rsaParameters.DP);

    WriteRSAParameter(writer, rsaParameters.DQ);

    WriteRSAParameter(writer, rsaParameters.InverseQ);



    writer.PopSequence();

    return MakePem(writer.Encode(), "RSA PRIVATE KEY");

}

Reading them back

.NET Core 3.0 built-in API

Except that .NET Core 3.0 doesn't understand PEM encoding, so you have to do PEM->binary yourself:

private const string RsaPrivateKey = "RSA PRIVATE KEY";

private const string SubjectPublicKeyInfo = "PUBLIC KEY";



private static byte PemToBer(string pem, string header)

{

    // Technically these should include a newline at the end,

    // and either newline-or-beginning-of-data at the beginning.

    string begin = $"-----BEGIN {header}-----";

    string end = $"-----END {header}-----";



    int beginIdx = pem.IndexOf(begin);

    int base64Start = beginIdx + begin.Length;

    int endIdx = pem.IndexOf(end, base64Start);



    return Convert.FromBase64String(pem.Substring(base64Start, endIdx - base64Start));

}

Once that's done you can now load the keys:

using (RSA rsa = RSA.Create())

{

    rsa.ImportRSAPrivateKey(PemToBer(pemPrivateKey, RsaPrivateKey), out _);



    ...

}



using (RSA rsa = RSA.Create())

{

    rsa.ImportSubjectPublicKeyInfo(PemToBer(pemPublicKey, SubjectPublicKeyInfo), out _);



    ...

}

Semi-manually

If you can't use .NET Core 3.0, but you can use pre-release NuGet packages, you can make use of the prototype ASN.1 reader package (which is the same code that's used internally in .NET Core 3.0; it's just that the API surface isn't finalized).

For the public key:

private static RSA FromSubjectPublicKeyInfo(string pem)

{

    AsnReader reader = new AsnReader(PemToBer(pem, SubjectPublicKeyInfo), AsnEncodingRules.DER);

    AsnReader spki = reader.ReadSequence();

    reader.ThrowIfNotEmpty();



    AsnReader algorithmId = spki.ReadSequence();



    if (algorithmId.ReadObjectIdentifierAsString() != "1.2.840.113549.1.1.1")

    {

        throw new InvalidOperationException();

    }



    algorithmId.ReadNull();

    algorithmId.ThrowIfNotEmpty();



    AsnReader rsaPublicKey = spki.ReadSequence();



    RSAParameters rsaParameters = new RSAParameters

    {

        Modulus = ReadNormalizedInteger(rsaPublicKey),

        Exponent = ReadNormalizedInteger(rsaPublicKey),

    };



    rsaPublicKey.ThrowIfNotEmpty();



    RSA rsa = RSA.Create();

    rsa.ImportParameters(rsaParameters);

    return rsa;

}



private static byte ReadNormalizedInteger(AsnReader reader)

{

    ReadOnlyMemory<byte> memory = reader.ReadIntegerBytes();

    ReadOnlySpan<byte> span = memory.Span;



    if (span[0] == 0)

    {

        span = span.Slice(1);

    }



    return span.ToArray();

}

And because the private key values have to have the correct size arrays, the private key one is just a little trickier:

private static RSA FromRSAPrivateKey(string pem)

{

    AsnReader reader = new AsnReader(PemToBer(pem, RsaPrivateKey), AsnEncodingRules.DER);

    AsnReader rsaPrivateKey = reader.ReadSequence();

    reader.ThrowIfNotEmpty();



    if (!rsaPrivateKey.TryReadInt32(out int version) || version != 0)

    {

        throw new InvalidOperationException();

    }



    byte modulus = ReadNormalizedInteger(rsaPrivateKey);

    int halfModulusLen = (modulus.Length + 1) / 2;



    RSAParameters rsaParameters = new RSAParameters

    {

        Modulus = modulus,

        Exponent = ReadNormalizedInteger(rsaPrivateKey),

        D = ReadNormalizedInteger(rsaPrivateKey, modulus.Length),

        P = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        Q = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        DP = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        DQ = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        InverseQ = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

    };



    rsaPrivateKey.ThrowIfNotEmpty();



    RSA rsa = RSA.Create();

    rsa.ImportParameters(rsaParameters);

    return rsa;

}



private static byte ReadNormalizedInteger(AsnReader reader, int length)

{

    ReadOnlyMemory<byte> memory = reader.ReadIntegerBytes();

    ReadOnlySpan<byte> span = memory.Span;



    if (span[0] == 0)

    {

        span = span.Slice(1);

    }



    byte buf = new byte[length];

    int skipSize = length - span.Length;

    span.CopyTo(buf.AsSpan(skipSize));

    return buf;

}

share|improve this answer

edited Jan 2 at 18:57

answered Jan 2 at 18:14

bartonjsbartonjs

13.9k12658

add a comment | 

1

Starting in .NET Core 3.0, this is (largely) built-in.

Writing SubjectPublicKeyInfo and RSAPrivateKey

.NET Core 3.0 built-in API

The output of the builtin API is the binary representation, to make them PEM you need to output the header, footer, and base64:

private static string MakePem(byte ber, string header)

{

    StringBuilder builder = new StringBuilder("-----BEGIN ");

    builder.Append(header);

    builder.AppendLine("-----");



    string base64 = Convert.ToBase64String(ber);

    int offset = 0;

    const int LineLength = 64;



    while (offset < base64.Length)

    {

        int lineEnd = Math.Min(offset + LineLength, base64.Length);

        builder.AppendLine(base64.Substring(offset, lineEnd - offset));

        offset = lineEnd;

    }



    builder.Append("-----END ");

    builder.Append(header);

    builder.AppendLine("-----");

    return builder.ToString();

}

So to produce the strings:

string publicKey = MakePem(rsa.ExportSubjectPublicKeyInfo(), "PUBLIC KEY");

string privateKey = MakePem(rsa.ExportRSAPrivateKey(), "RSA PRIVATE KEY");

Semi-manually

If you can't use .NET Core 3.0, but you can use pre-release NuGet packages, you can make use of the prototype ASN.1 writer package (which is the same code that's used internally in .NET Core 3.0; it's just that the API surface isn't finalized).

To make the public key:

private static string ToSubjectPublicKeyInfo(RSA rsa)

{

    RSAParameters rsaParameters = rsa.ExportParameters(false);



    AsnWriter writer = new AsnWriter(AsnEncodingRules.DER);

    writer.PushSequence();



    writer.PushSequence();

    writer.WriteObjectIdentifier("1.2.840.113549.1.1.1");

    writer.WriteNull();

    writer.PopSequence();



    AsnWriter innerWriter = new AsnWriter(AsnEncodingRules.DER);



    innerWriter.PushSequence();

    WriteRSAParameter(innerWriter, rsaParameters.Modulus);

    WriteRSAParameter(innerWriter, rsaParameters.Exponent);

    innerWriter.PopSequence();



    writer.WriteBitString(innerWriter.Encode());



    writer.PopSequence();

    return MakePem(writer.Encode(), "PUBLIC KEY");

}

And to make the private key:

private static string ToRSAPrivateKey(RSA rsa)

{

    RSAParameters rsaParameters = rsa.ExportParameters(true);



    AsnWriter writer = new AsnWriter(AsnEncodingRules.DER);

    writer.PushSequence();



    writer.WriteInteger(0);

    WriteRSAParameter(writer, rsaParameters.Modulus);

    WriteRSAParameter(writer, rsaParameters.Exponent);

    WriteRSAParameter(writer, rsaParameters.D);

    WriteRSAParameter(writer, rsaParameters.P);

    WriteRSAParameter(writer, rsaParameters.Q);

    WriteRSAParameter(writer, rsaParameters.DP);

    WriteRSAParameter(writer, rsaParameters.DQ);

    WriteRSAParameter(writer, rsaParameters.InverseQ);



    writer.PopSequence();

    return MakePem(writer.Encode(), "RSA PRIVATE KEY");

}

Reading them back

.NET Core 3.0 built-in API

Except that .NET Core 3.0 doesn't understand PEM encoding, so you have to do PEM->binary yourself:

private const string RsaPrivateKey = "RSA PRIVATE KEY";

private const string SubjectPublicKeyInfo = "PUBLIC KEY";



private static byte PemToBer(string pem, string header)

{

    // Technically these should include a newline at the end,

    // and either newline-or-beginning-of-data at the beginning.

    string begin = $"-----BEGIN {header}-----";

    string end = $"-----END {header}-----";



    int beginIdx = pem.IndexOf(begin);

    int base64Start = beginIdx + begin.Length;

    int endIdx = pem.IndexOf(end, base64Start);



    return Convert.FromBase64String(pem.Substring(base64Start, endIdx - base64Start));

}

Once that's done you can now load the keys:

using (RSA rsa = RSA.Create())

{

    rsa.ImportRSAPrivateKey(PemToBer(pemPrivateKey, RsaPrivateKey), out _);



    ...

}



using (RSA rsa = RSA.Create())

{

    rsa.ImportSubjectPublicKeyInfo(PemToBer(pemPublicKey, SubjectPublicKeyInfo), out _);



    ...

}

Semi-manually

If you can't use .NET Core 3.0, but you can use pre-release NuGet packages, you can make use of the prototype ASN.1 reader package (which is the same code that's used internally in .NET Core 3.0; it's just that the API surface isn't finalized).

For the public key:

private static RSA FromSubjectPublicKeyInfo(string pem)

{

    AsnReader reader = new AsnReader(PemToBer(pem, SubjectPublicKeyInfo), AsnEncodingRules.DER);

    AsnReader spki = reader.ReadSequence();

    reader.ThrowIfNotEmpty();



    AsnReader algorithmId = spki.ReadSequence();



    if (algorithmId.ReadObjectIdentifierAsString() != "1.2.840.113549.1.1.1")

    {

        throw new InvalidOperationException();

    }



    algorithmId.ReadNull();

    algorithmId.ThrowIfNotEmpty();



    AsnReader rsaPublicKey = spki.ReadSequence();



    RSAParameters rsaParameters = new RSAParameters

    {

        Modulus = ReadNormalizedInteger(rsaPublicKey),

        Exponent = ReadNormalizedInteger(rsaPublicKey),

    };



    rsaPublicKey.ThrowIfNotEmpty();



    RSA rsa = RSA.Create();

    rsa.ImportParameters(rsaParameters);

    return rsa;

}



private static byte ReadNormalizedInteger(AsnReader reader)

{

    ReadOnlyMemory<byte> memory = reader.ReadIntegerBytes();

    ReadOnlySpan<byte> span = memory.Span;



    if (span[0] == 0)

    {

        span = span.Slice(1);

    }



    return span.ToArray();

}

And because the private key values have to have the correct size arrays, the private key one is just a little trickier:

private static RSA FromRSAPrivateKey(string pem)

{

    AsnReader reader = new AsnReader(PemToBer(pem, RsaPrivateKey), AsnEncodingRules.DER);

    AsnReader rsaPrivateKey = reader.ReadSequence();

    reader.ThrowIfNotEmpty();



    if (!rsaPrivateKey.TryReadInt32(out int version) || version != 0)

    {

        throw new InvalidOperationException();

    }



    byte modulus = ReadNormalizedInteger(rsaPrivateKey);

    int halfModulusLen = (modulus.Length + 1) / 2;



    RSAParameters rsaParameters = new RSAParameters

    {

        Modulus = modulus,

        Exponent = ReadNormalizedInteger(rsaPrivateKey),

        D = ReadNormalizedInteger(rsaPrivateKey, modulus.Length),

        P = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        Q = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        DP = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        DQ = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        InverseQ = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

    };



    rsaPrivateKey.ThrowIfNotEmpty();



    RSA rsa = RSA.Create();

    rsa.ImportParameters(rsaParameters);

    return rsa;

}



private static byte ReadNormalizedInteger(AsnReader reader, int length)

{

    ReadOnlyMemory<byte> memory = reader.ReadIntegerBytes();

    ReadOnlySpan<byte> span = memory.Span;



    if (span[0] == 0)

    {

        span = span.Slice(1);

    }



    byte buf = new byte[length];

    int skipSize = length - span.Length;

    span.CopyTo(buf.AsSpan(skipSize));

    return buf;

}

share|improve this answer

edited Jan 2 at 18:57

answered Jan 2 at 18:14

bartonjsbartonjs

13.9k12658

add a comment | 

1

1

1

Starting in .NET Core 3.0, this is (largely) built-in.

Writing SubjectPublicKeyInfo and RSAPrivateKey

.NET Core 3.0 built-in API

The output of the builtin API is the binary representation, to make them PEM you need to output the header, footer, and base64:

private static string MakePem(byte ber, string header)

{

    StringBuilder builder = new StringBuilder("-----BEGIN ");

    builder.Append(header);

    builder.AppendLine("-----");



    string base64 = Convert.ToBase64String(ber);

    int offset = 0;

    const int LineLength = 64;



    while (offset < base64.Length)

    {

        int lineEnd = Math.Min(offset + LineLength, base64.Length);

        builder.AppendLine(base64.Substring(offset, lineEnd - offset));

        offset = lineEnd;

    }



    builder.Append("-----END ");

    builder.Append(header);

    builder.AppendLine("-----");

    return builder.ToString();

}

So to produce the strings:

string publicKey = MakePem(rsa.ExportSubjectPublicKeyInfo(), "PUBLIC KEY");

string privateKey = MakePem(rsa.ExportRSAPrivateKey(), "RSA PRIVATE KEY");

Semi-manually

If you can't use .NET Core 3.0, but you can use pre-release NuGet packages, you can make use of the prototype ASN.1 writer package (which is the same code that's used internally in .NET Core 3.0; it's just that the API surface isn't finalized).

To make the public key:

private static string ToSubjectPublicKeyInfo(RSA rsa)

{

    RSAParameters rsaParameters = rsa.ExportParameters(false);



    AsnWriter writer = new AsnWriter(AsnEncodingRules.DER);

    writer.PushSequence();



    writer.PushSequence();

    writer.WriteObjectIdentifier("1.2.840.113549.1.1.1");

    writer.WriteNull();

    writer.PopSequence();



    AsnWriter innerWriter = new AsnWriter(AsnEncodingRules.DER);



    innerWriter.PushSequence();

    WriteRSAParameter(innerWriter, rsaParameters.Modulus);

    WriteRSAParameter(innerWriter, rsaParameters.Exponent);

    innerWriter.PopSequence();



    writer.WriteBitString(innerWriter.Encode());



    writer.PopSequence();

    return MakePem(writer.Encode(), "PUBLIC KEY");

}

And to make the private key:

private static string ToRSAPrivateKey(RSA rsa)

{

    RSAParameters rsaParameters = rsa.ExportParameters(true);



    AsnWriter writer = new AsnWriter(AsnEncodingRules.DER);

    writer.PushSequence();



    writer.WriteInteger(0);

    WriteRSAParameter(writer, rsaParameters.Modulus);

    WriteRSAParameter(writer, rsaParameters.Exponent);

    WriteRSAParameter(writer, rsaParameters.D);

    WriteRSAParameter(writer, rsaParameters.P);

    WriteRSAParameter(writer, rsaParameters.Q);

    WriteRSAParameter(writer, rsaParameters.DP);

    WriteRSAParameter(writer, rsaParameters.DQ);

    WriteRSAParameter(writer, rsaParameters.InverseQ);



    writer.PopSequence();

    return MakePem(writer.Encode(), "RSA PRIVATE KEY");

}

Reading them back

.NET Core 3.0 built-in API

Except that .NET Core 3.0 doesn't understand PEM encoding, so you have to do PEM->binary yourself:

private const string RsaPrivateKey = "RSA PRIVATE KEY";

private const string SubjectPublicKeyInfo = "PUBLIC KEY";



private static byte PemToBer(string pem, string header)

{

    // Technically these should include a newline at the end,

    // and either newline-or-beginning-of-data at the beginning.

    string begin = $"-----BEGIN {header}-----";

    string end = $"-----END {header}-----";



    int beginIdx = pem.IndexOf(begin);

    int base64Start = beginIdx + begin.Length;

    int endIdx = pem.IndexOf(end, base64Start);



    return Convert.FromBase64String(pem.Substring(base64Start, endIdx - base64Start));

}

Once that's done you can now load the keys:

using (RSA rsa = RSA.Create())

{

    rsa.ImportRSAPrivateKey(PemToBer(pemPrivateKey, RsaPrivateKey), out _);



    ...

}



using (RSA rsa = RSA.Create())

{

    rsa.ImportSubjectPublicKeyInfo(PemToBer(pemPublicKey, SubjectPublicKeyInfo), out _);



    ...

}

Semi-manually

If you can't use .NET Core 3.0, but you can use pre-release NuGet packages, you can make use of the prototype ASN.1 reader package (which is the same code that's used internally in .NET Core 3.0; it's just that the API surface isn't finalized).

For the public key:

private static RSA FromSubjectPublicKeyInfo(string pem)

{

    AsnReader reader = new AsnReader(PemToBer(pem, SubjectPublicKeyInfo), AsnEncodingRules.DER);

    AsnReader spki = reader.ReadSequence();

    reader.ThrowIfNotEmpty();



    AsnReader algorithmId = spki.ReadSequence();



    if (algorithmId.ReadObjectIdentifierAsString() != "1.2.840.113549.1.1.1")

    {

        throw new InvalidOperationException();

    }



    algorithmId.ReadNull();

    algorithmId.ThrowIfNotEmpty();



    AsnReader rsaPublicKey = spki.ReadSequence();



    RSAParameters rsaParameters = new RSAParameters

    {

        Modulus = ReadNormalizedInteger(rsaPublicKey),

        Exponent = ReadNormalizedInteger(rsaPublicKey),

    };



    rsaPublicKey.ThrowIfNotEmpty();



    RSA rsa = RSA.Create();

    rsa.ImportParameters(rsaParameters);

    return rsa;

}



private static byte ReadNormalizedInteger(AsnReader reader)

{

    ReadOnlyMemory<byte> memory = reader.ReadIntegerBytes();

    ReadOnlySpan<byte> span = memory.Span;



    if (span[0] == 0)

    {

        span = span.Slice(1);

    }



    return span.ToArray();

}

And because the private key values have to have the correct size arrays, the private key one is just a little trickier:

private static RSA FromRSAPrivateKey(string pem)

{

    AsnReader reader = new AsnReader(PemToBer(pem, RsaPrivateKey), AsnEncodingRules.DER);

    AsnReader rsaPrivateKey = reader.ReadSequence();

    reader.ThrowIfNotEmpty();



    if (!rsaPrivateKey.TryReadInt32(out int version) || version != 0)

    {

        throw new InvalidOperationException();

    }



    byte modulus = ReadNormalizedInteger(rsaPrivateKey);

    int halfModulusLen = (modulus.Length + 1) / 2;



    RSAParameters rsaParameters = new RSAParameters

    {

        Modulus = modulus,

        Exponent = ReadNormalizedInteger(rsaPrivateKey),

        D = ReadNormalizedInteger(rsaPrivateKey, modulus.Length),

        P = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        Q = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        DP = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        DQ = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        InverseQ = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

    };



    rsaPrivateKey.ThrowIfNotEmpty();



    RSA rsa = RSA.Create();

    rsa.ImportParameters(rsaParameters);

    return rsa;

}



private static byte ReadNormalizedInteger(AsnReader reader, int length)

{

    ReadOnlyMemory<byte> memory = reader.ReadIntegerBytes();

    ReadOnlySpan<byte> span = memory.Span;



    if (span[0] == 0)

    {

        span = span.Slice(1);

    }



    byte buf = new byte[length];

    int skipSize = length - span.Length;

    span.CopyTo(buf.AsSpan(skipSize));

    return buf;

}

share|improve this answer

edited Jan 2 at 18:57

answered Jan 2 at 18:14

bartonjsbartonjs

13.9k12658

Starting in .NET Core 3.0, this is (largely) built-in.

Writing SubjectPublicKeyInfo and RSAPrivateKey

.NET Core 3.0 built-in API

The output of the builtin API is the binary representation, to make them PEM you need to output the header, footer, and base64:

private static string MakePem(byte ber, string header)

{

    StringBuilder builder = new StringBuilder("-----BEGIN ");

    builder.Append(header);

    builder.AppendLine("-----");



    string base64 = Convert.ToBase64String(ber);

    int offset = 0;

    const int LineLength = 64;



    while (offset < base64.Length)

    {

        int lineEnd = Math.Min(offset + LineLength, base64.Length);

        builder.AppendLine(base64.Substring(offset, lineEnd - offset));

        offset = lineEnd;

    }



    builder.Append("-----END ");

    builder.Append(header);

    builder.AppendLine("-----");

    return builder.ToString();

}

So to produce the strings:

string publicKey = MakePem(rsa.ExportSubjectPublicKeyInfo(), "PUBLIC KEY");

string privateKey = MakePem(rsa.ExportRSAPrivateKey(), "RSA PRIVATE KEY");

Semi-manually

If you can't use .NET Core 3.0, but you can use pre-release NuGet packages, you can make use of the prototype ASN.1 writer package (which is the same code that's used internally in .NET Core 3.0; it's just that the API surface isn't finalized).

To make the public key:

private static string ToSubjectPublicKeyInfo(RSA rsa)

{

    RSAParameters rsaParameters = rsa.ExportParameters(false);



    AsnWriter writer = new AsnWriter(AsnEncodingRules.DER);

    writer.PushSequence();



    writer.PushSequence();

    writer.WriteObjectIdentifier("1.2.840.113549.1.1.1");

    writer.WriteNull();

    writer.PopSequence();



    AsnWriter innerWriter = new AsnWriter(AsnEncodingRules.DER);



    innerWriter.PushSequence();

    WriteRSAParameter(innerWriter, rsaParameters.Modulus);

    WriteRSAParameter(innerWriter, rsaParameters.Exponent);

    innerWriter.PopSequence();



    writer.WriteBitString(innerWriter.Encode());



    writer.PopSequence();

    return MakePem(writer.Encode(), "PUBLIC KEY");

}

And to make the private key:

private static string ToRSAPrivateKey(RSA rsa)

{

    RSAParameters rsaParameters = rsa.ExportParameters(true);



    AsnWriter writer = new AsnWriter(AsnEncodingRules.DER);

    writer.PushSequence();



    writer.WriteInteger(0);

    WriteRSAParameter(writer, rsaParameters.Modulus);

    WriteRSAParameter(writer, rsaParameters.Exponent);

    WriteRSAParameter(writer, rsaParameters.D);

    WriteRSAParameter(writer, rsaParameters.P);

    WriteRSAParameter(writer, rsaParameters.Q);

    WriteRSAParameter(writer, rsaParameters.DP);

    WriteRSAParameter(writer, rsaParameters.DQ);

    WriteRSAParameter(writer, rsaParameters.InverseQ);



    writer.PopSequence();

    return MakePem(writer.Encode(), "RSA PRIVATE KEY");

}

Reading them back

.NET Core 3.0 built-in API

Except that .NET Core 3.0 doesn't understand PEM encoding, so you have to do PEM->binary yourself:

private const string RsaPrivateKey = "RSA PRIVATE KEY";

private const string SubjectPublicKeyInfo = "PUBLIC KEY";



private static byte PemToBer(string pem, string header)

{

    // Technically these should include a newline at the end,

    // and either newline-or-beginning-of-data at the beginning.

    string begin = $"-----BEGIN {header}-----";

    string end = $"-----END {header}-----";



    int beginIdx = pem.IndexOf(begin);

    int base64Start = beginIdx + begin.Length;

    int endIdx = pem.IndexOf(end, base64Start);



    return Convert.FromBase64String(pem.Substring(base64Start, endIdx - base64Start));

}

Once that's done you can now load the keys:

using (RSA rsa = RSA.Create())

{

    rsa.ImportRSAPrivateKey(PemToBer(pemPrivateKey, RsaPrivateKey), out _);



    ...

}



using (RSA rsa = RSA.Create())

{

    rsa.ImportSubjectPublicKeyInfo(PemToBer(pemPublicKey, SubjectPublicKeyInfo), out _);



    ...

}

Semi-manually

If you can't use .NET Core 3.0, but you can use pre-release NuGet packages, you can make use of the prototype ASN.1 reader package (which is the same code that's used internally in .NET Core 3.0; it's just that the API surface isn't finalized).

For the public key:

private static RSA FromSubjectPublicKeyInfo(string pem)

{

    AsnReader reader = new AsnReader(PemToBer(pem, SubjectPublicKeyInfo), AsnEncodingRules.DER);

    AsnReader spki = reader.ReadSequence();

    reader.ThrowIfNotEmpty();



    AsnReader algorithmId = spki.ReadSequence();



    if (algorithmId.ReadObjectIdentifierAsString() != "1.2.840.113549.1.1.1")

    {

        throw new InvalidOperationException();

    }



    algorithmId.ReadNull();

    algorithmId.ThrowIfNotEmpty();



    AsnReader rsaPublicKey = spki.ReadSequence();



    RSAParameters rsaParameters = new RSAParameters

    {

        Modulus = ReadNormalizedInteger(rsaPublicKey),

        Exponent = ReadNormalizedInteger(rsaPublicKey),

    };



    rsaPublicKey.ThrowIfNotEmpty();



    RSA rsa = RSA.Create();

    rsa.ImportParameters(rsaParameters);

    return rsa;

}



private static byte ReadNormalizedInteger(AsnReader reader)

{

    ReadOnlyMemory<byte> memory = reader.ReadIntegerBytes();

    ReadOnlySpan<byte> span = memory.Span;



    if (span[0] == 0)

    {

        span = span.Slice(1);

    }



    return span.ToArray();

}

And because the private key values have to have the correct size arrays, the private key one is just a little trickier:

private static RSA FromRSAPrivateKey(string pem)

{

    AsnReader reader = new AsnReader(PemToBer(pem, RsaPrivateKey), AsnEncodingRules.DER);

    AsnReader rsaPrivateKey = reader.ReadSequence();

    reader.ThrowIfNotEmpty();



    if (!rsaPrivateKey.TryReadInt32(out int version) || version != 0)

    {

        throw new InvalidOperationException();

    }



    byte modulus = ReadNormalizedInteger(rsaPrivateKey);

    int halfModulusLen = (modulus.Length + 1) / 2;



    RSAParameters rsaParameters = new RSAParameters

    {

        Modulus = modulus,

        Exponent = ReadNormalizedInteger(rsaPrivateKey),

        D = ReadNormalizedInteger(rsaPrivateKey, modulus.Length),

        P = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        Q = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        DP = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        DQ = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

        InverseQ = ReadNormalizedInteger(rsaPrivateKey, halfModulusLen),

    };



    rsaPrivateKey.ThrowIfNotEmpty();



    RSA rsa = RSA.Create();

    rsa.ImportParameters(rsaParameters);

    return rsa;

}



private static byte ReadNormalizedInteger(AsnReader reader, int length)

{

    ReadOnlyMemory<byte> memory = reader.ReadIntegerBytes();

    ReadOnlySpan<byte> span = memory.Span;



    if (span[0] == 0)

    {

        span = span.Slice(1);

    }



    byte buf = new byte[length];

    int skipSize = length - span.Length;

    span.CopyTo(buf.AsSpan(skipSize));

    return buf;

}

share|improve this answer

edited Jan 2 at 18:57

answered Jan 2 at 18:14

bartonjsbartonjs

13.9k12658

share|improve this answer

share|improve this answer

edited Jan 2 at 18:57

edited Jan 2 at 18:57

edited Jan 2 at 18:57

answered Jan 2 at 18:14

bartonjsbartonjs

13.9k12658

answered Jan 2 at 18:14

bartonjsbartonjs

13.9k12658

answered Jan 2 at 18:14

bartonjsbartonjs

13.9k12658

13.9k12658

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