使用Bouncy Castle生成用于DH密钥交换的64字节公钥

Question

I need to generate a key pair for Diffie-Hellman key exchange using the secp256r1 curve using Bouncy Castle in C#. The public key should be 64 bytes (I'm not sure which format this is (compressed?), but I can find out).

I have the following code, but the lack of Bouncy Castle documentation has me lost.

X9ECParameters ecParams = SecNamedCurves.GetByName("secp256r1");
var spec = new ECDomainParameters(ecParams.Curve, ecParams.G, ecParams.N, ecParams.H, ecParams.GetSeed());
var keyGenParams = new ECKeyGenerationParameters(spec, new SecureRandom());

var keyGen = new ECKeyPairGenerator("ECDH");
keyGen.Init(keyGenParams);
AsymmetricCipherKeyPair keyPair = keyGen.GenerateKeyPair();
var pubKeyInfo = SubjectPublicKeyInfoFactory.CreateSubjectPublicKeyInfo(keyPair.Public);

// pubKeyInfo.GetDerEncoded()
// pubKeyInfo.GetEncoded()
// pubKeyInfo.PublicKey
// pubKeyInfo.ToAsn1Object()

From here, I have access to a lot of different export formats (seen above), but most values end up being 335 bytes long. pubKeyInfo.PublicKeyData.GetBytes() gives 65 bytes, but I'm not sure why.

I must have some basic misunderstanding here. What am I missing?

If it helps, another client uses the uECC_make_key function to generate the key pair.

Answer 1

I believe the data is provided by pubKeyInfo.PublicKeyData.GetBytes() . It's 65 bytes long because it has a prefix 0x04 byte indicating that the remaining 64 bytes describe the public key in uncompressed format (vs. 0x02 indicating compressed format).

See here for some discussion.