从 .NET Core 3.0 开始，这是（大部分）内置的。
编写 SubjectPublicKeyInfo 和 RSAPrivateKey
.NET Core 3.0 内置 API
内置 API 的输出是二进制表示，要使它们成为 PEM，您需要输出页眉、页脚和 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();
}
所以要产生字符串：
string publicKey = MakePem(rsa.ExportSubjectPublicKeyInfo(), "PUBLIC KEY");
string privateKey = MakePem(rsa.ExportRSAPrivateKey(), "RSA PRIVATE KEY");
半手动
如果您不能使用 .NET Core 3.0，但可以使用预发布的 NuGet 包，则可以使用 prototype ASN.1 writer package（与 .NET Core 3.0 内部使用的代码相同；只是API 表面尚未最终确定）。
制作公钥：
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");
}
并制作私钥：
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");
}
回读它们
.NET Core 3.0 内置 API
除了.NET Core 3.0不理解PEM编码，所以要自己做PEM->binary：
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));
}
完成后，您现在可以加载密钥：
using (RSA rsa = RSA.Create())
{
rsa.ImportRSAPrivateKey(PemToBer(pemPrivateKey, RsaPrivateKey), out _);
...
}
using (RSA rsa = RSA.Create())
{
rsa.ImportSubjectPublicKeyInfo(PemToBer(pemPublicKey, SubjectPublicKeyInfo), out _);
...
}
半手动
如果您不能使用 .NET Core 3.0，但可以使用预发布的 NuGet 包，则可以使用 prototype ASN.1 reader package（与 .NET Core 3.0 内部使用的代码相同；只是API 表面尚未最终确定）。
对于公钥：
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();
}
而且由于私钥值必须具有正确大小的数组，所以私钥值有点棘手：
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;
}