我想使用Diffie hellman在c#Server和c Client之间生成密钥。此代码为服务器生成公钥：

        serverECDH = new ECDiffieHellmanCng(ECCurve.NamedCurves.nistP256);
        serverECDH.KeyDerivationFunction = ECDiffieHellmanKeyDerivationFunction.Hash;
        serverECDH.HashAlgorithm = CngAlgorithm.Sha256; 
        ECDHPublicKey =Convert.ToBase64String(serverECDH.PublicKey.ToByteArray());
        Console.WriteLine(serverECDH.KeySize); //256
        Console.WriteLine(serverECDH.PublicKey.ToByteArray().Length); //72
        Console.WriteLine(ECDHPublicKey);

我想知道为什么public Key Byte Array Size是72，而我期望是64字节长的数组？此外，这是我在Client中生成公钥的实现：

if (NULL == (pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_EC, NULL))) HandleErrors(1);
if (1 != EVP_PKEY_paramgen_init(pctx)) HandleErrors(2);
if (1 != EVP_PKEY_CTX_set_ec_paramgen_curve_nid(pctx, NID_X9_62_prime256v1)) HandleErrors(3);

if (!EVP_PKEY_paramgen(pctx, &params)) HandleErrors(4);
if (NULL == (kctx = EVP_PKEY_CTX_new(params, NULL))) HandleErrors(5);

if (1 != EVP_PKEY_keygen_init(kctx)) HandleErrors(6);
if (1 != EVP_PKEY_keygen(kctx, &pkey)) HandleErrors(7);

bio = BIO_new(BIO_s_mem());
PEM_write_bio_PUBKEY(bio, pkey);
int publicKeyLen = BIO_pending(bio);
cout << publicKeyLen << endl;
unsigned char* publicKeyChar = (unsigned char*)malloc(publicKeyLen);
BIO_read(bio, publicKeyChar, publicKeyLen);

ECDHPublicKey =  string(reinterpret_cast<char const*>(publicKeyChar),publicKeyLen);
cout << ECDHPublicKey << endl;

在这段代码中，公钥长度是128字节（字符？）这又是奇怪的，因为我指定NID_X9_62_prime256v1曲线。我的错误在哪里？此外，NID_X9_62_prime256v1和nistP256在c和c#中匹配吗？

编辑：这是cout的一个例子

-----BEGIN PUBLIC KEY-----MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEUFD9ZNby6x2bf/VC16/NHSxIXdit Ips60uLoi0/jKmbmMHRg2xbXVzV8Uc1DElMlZA817bMFCnVvi1VsM5JYg==

-----结束公钥-----