I am looking to convert an RSA public key into something that I could use as an SSH public key.
Currently I have Bouncy Castle producing me a public key that looks like this:
-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAq1Y5300i8bN+cI2U3wJE
Kh3xG/.........jbuz+WB0vvG
P25UwCle2k5siVMwbImEYsr+Xt0dsMmGVB3/6MHAqrM3QQdQ8p2E5TyzL+JYa1FT
gwIDAQAB
-----END PUBLIC KEY-----
I want it to have an RFC 4716 format similar to this:
ssh-rsa AAAAB3NzaC1yc2.......G1p2Ag3mZLFsks7RNHVLgMsGIAikQ==
My Code so far using Bouncy Castle looks like this:
var r = new Org.BouncyCastle.Crypto.Generators.RsaKeyPairGenerator();
r.Init(new KeyGenerationParameters(new SecureRandom(), 2048));
var keys = r.GenerateKeyPair();
var stringWriter = new StringWriter();
var pemWriter = new PemWriter(stringWriter);
pemWriter.WriteObject(keys.Private);
pemWriter.Writer.Flush();
stringWriter.Close();
PrivateKey = stringWriter.ToString();
stringWriter = new StringWriter();
pemWriter = new PemWriter(stringWriter);
pemWriter.WriteObject(keys.Public);
pemWriter.Writer.Flush();
stringWriter.Close();
PublicKey = stringWriter.ToString();
How do I reformat and encode the key to make it look like this?
Has anyone created SSH public keys with Bouncy Castle or similar?
I found no ready-to-use function for this in BouncyCastle. So, the workaround is to use PemReader
and then format the result. The result will be available as PublicSSH
property:
using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Crypto.Generators;
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Math;
using Org.BouncyCastle.OpenSsl;
using Org.BouncyCastle.Security;
using System;
using System.IO;
using System.Text;
namespace Deploy4Me.Common.Utils
{
public class RSAKey
{
public string PublicPEM { get; set; }
public string PrivatePEM { get; set; }
public string PublicSSH { get; set; }
}
public static class RSA
{
public static RSAKey Generate()
{
try
{
RSAKey result = new RSAKey();
IAsymmetricCipherKeyPairGenerator gen;
KeyGenerationParameters param;
gen = new RsaKeyPairGenerator();
param = new RsaKeyGenerationParameters(
BigInteger.ValueOf(3L),
new SecureRandom(),
2048,
80
);
gen.Init(param);
AsymmetricCipherKeyPair pair = gen.GenerateKeyPair();
using(TextWriter textWriter = new StringWriter())
{
PemWriter wr = new PemWriter(textWriter);
wr.WriteObject(pair.Private);
wr.Writer.Flush();
result.PrivatePEM = textWriter.ToString();
}
using (TextWriter textWriter = new StringWriter())
{
PemWriter wr = new PemWriter(textWriter);
wr.WriteObject(pair.Public);
wr.Writer.Flush();
result.PublicPEM = textWriter.ToString();
}
using (StringReader sr = new StringReader(result.PublicPEM))
{
PemReader reader = new PemReader(sr);
RsaKeyParameters r = (RsaKeyParameters)reader.ReadObject();
byte[] sshrsa_bytes = Encoding.Default.GetBytes("ssh-rsa");
byte[] n = r.Modulus.ToByteArray();
byte[] e = r.Exponent.ToByteArray();
string buffer64;
using(MemoryStream ms = new MemoryStream()){
ms.Write(ToBytes(sshrsa_bytes.Length), 0, 4);
ms.Write(sshrsa_bytes, 0, sshrsa_bytes.Length);
ms.Write(ToBytes(e.Length), 0, 4);
ms.Write(e, 0, e.Length);
ms.Write(ToBytes(n.Length), 0, 4);
ms.Write(n, 0, n.Length);
ms.Flush();
buffer64 = Convert.ToBase64String(ms.ToArray());
}
result.PublicSSH = string.Format("ssh-rsa {0} generated-key", buffer64);
}
return result;
}
catch (Org.BouncyCastle.Crypto.CryptoException ex)
{
throw ex;
}
}
private static byte[] ToBytes(int i)
{
byte[] bts = BitConverter.GetBytes(i);
if (BitConverter.IsLittleEndian)
{
Array.Reverse(bts);
}
return bts;
}
}
}
Note: I work at Microsoft but this is not a Microsoft Answer, just Personal.
Adding to Pavels Answer,
I've found that for some reason when generating a 3072 Bit RSA key, PuttyGen would generate a different RSA public key than mine.
After researching, I found that it seems in the source code of the Putty Gen Program it would do .Length + 1 to the Byte array, adding a leading 0.
For the BouncyCastle, you would change this line.
ms.Write(ToBytes(n.Length), 0, 4);
ms.Write(n, 0, n.Length);
to
ms.Write(ToBytes(n.Length+1), 0, 4);//Add +1 to Emulate PuttyGen
ms.Write(new byte[] { 0 }, 0, 1); //Add a 0 to Emulate PuttyGen
ms.Write(n, 0, n.Length);
For Microsoft .net RSACryptoServiceProvider it would look like this
RSACryptoServiceProvider RSA = new RSACryptoServiceProvider(3072);
byte[] sshrsa_bytes = Encoding.Default.GetBytes("ssh-rsa");
byte[] n = RSA.ExportParameters(false).Modulus;
byte[] e = RSA.ExportParameters(false).Exponent;
string buffer64;
using (MemoryStream ms = new MemoryStream())
{
ms.Write(ToBytes(sshrsa_bytes.Length), 0, 4);
ms.Write(sshrsa_bytes, 0, sshrsa_bytes.Length);
ms.Write(ToBytes(e.Length), 0, 4);
ms.Write(e, 0, e.Length);
ms.Write(ToBytes(n.Length+1), 0, 4); //Remove the +1 if not Emulating Putty Gen
ms.Write(new byte[] { 0 }, 0, 1); //Add a 0 to Emulate PuttyGen
ms.Write(n, 0, n.Length);
ms.Flush();
buffer64 = Convert.ToBase64String(ms.ToArray());
}
string pubssh = string.Format("ssh-rsa {0} generated-key", buffer64);
You can see my Private Key I used for testing & the putty gen source code link https://www.cameronmoten.com/2017/12/21/rsacryptoserviceprovider-create-a-ssh-rsa-public-key/
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