/// <summary>
/// Returns PEM encoded RSA PublicKey
/// </summary>
/// <param name="key">CngKey containing RSA PublicKey</param>
/// <returns>PEM encoded PublicKey</returns>
public static string ExportToPem(CngKey key)
{
RSACng rsaCng = new RSACng(key);
RSAParameters parameters = rsaCng.ExportParameters(false);
byte[] modulusBytes = DerUtils.EncodeUnsignedInteger(parameters.Modulus);
byte[] exponentBytes = DerUtils.EncodeUnsignedInteger(parameters.Exponent);
byte[] dataSeqBytes = DerUtils.EncodeSequenceOf(new List <byte[]> {
modulusBytes, exponentBytes
});
byte[] bitStringBytes = DerUtils.EncodeBitString(dataSeqBytes, 0);
byte[] oidBytes = DerUtils.EncodeOid(RSA_ENCRYPTION_OID);
byte[] oidSeqBytes = DerUtils.EncodeSequenceOf(new List <byte[]> {
oidBytes, DerUtils.EncodeNull()
});
byte[] derBytes = DerUtils.EncodeSequenceOf(new List <byte[]> {
oidSeqBytes, bitStringBytes
});
char[] derB64 = Convert.ToBase64String(derBytes, 0, (int)derBytes.Length).ToCharArray();
TextWriter outputWriter = new StringWriter();
outputWriter.WriteLine(PEM_PUBLIC_KEY_HEADER);
for (var i = 0; i < derB64.Length; i += 64)
{
outputWriter.WriteLine(derB64, i, Math.Min(64, derB64.Length - i));
}
outputWriter.WriteLine(PEM_PUBLIC_KEY_FOOTER);
return(outputWriter.ToString());
}
/// <summary>
/// Decodes a PEM RSA public key file
/// </summary>
/// <param name="filePath">The path to the PEM file</param>
/// <returns>A CngKey object that constains the public key from the PEM file</returns>
public static CngKey ImportFromPem(string filePath)
{
string pemStr;
using (StreamReader fileStream = File.OpenText(filePath))
{
pemStr = fileStream.ReadToEnd();
}
if (!pemStr.StartsWith(PEM_PUBLIC_KEY_HEADER))
{
throw new FileFormatException("Not a public key PEM file. PEM Header formatted incorrectly.");
}
StringBuilder pemB64 = new StringBuilder(pemStr);
pemB64.Replace(PEM_PUBLIC_KEY_HEADER, "").Replace(PEM_PUBLIC_KEY_FOOTER, "");
byte[] derBytes = Convert.FromBase64String(pemB64.ToString());
List <byte[]> mainBodySeqBytes = DerUtils.DecodeSequenceOf(derBytes);
List <byte[]> oidSeqBytes = DerUtils.DecodeSequenceOf(mainBodySeqBytes[0]);
if (DerUtils.DecodeOid(oidSeqBytes[0]) != RSA_ENCRYPTION_OID)
{
throw new FileFormatException("Not labelled as a public key OID.");
}
DerUtils.DecodeNull(oidSeqBytes[1]);
byte[] bitStringBytes = DerUtils.DecodeBitstring(mainBodySeqBytes[1], out _);
List <byte[]> dataSeqBytes = DerUtils.DecodeSequenceOf(bitStringBytes);
byte[] modulusBytes = DerUtils.DecodeUnsignedInteger(dataSeqBytes[0]);
byte[] exponenBytes = DerUtils.DecodeUnsignedInteger(dataSeqBytes[1]);
RSACng rsaCng = new RSACng();
RSAParameters rsaParams = new RSAParameters();
rsaParams.Modulus = modulusBytes;
rsaParams.Exponent = exponenBytes;
rsaCng.ImportParameters(rsaParams);
return(rsaCng.Key);
}
