我需要生成一个EC Diffie Hellman密钥对。我使用的是命名曲线secp256r1和OpenSSL。以下是目前我拥有的:
unsigned char *ecdh(size_t *secret_len)
{
EVP_PKEY_CTX *pctx, *kctx;
EVP_PKEY_CTX *ctx;
unsigned char *secret;
EVP_PKEY *pkey = NULL, *peerkey, *params = NULL;
/* NB: assumes pkey, peerkey have been already set up */
/* Create the context for parameter generation */
if(NULL == (pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_EC, NULL)))
printf("Error in EC key generation\n");
/* Initialise the parameter generation */
if(1 != EVP_PKEY_paramgen_init(pctx))
printf("Error in EC key generation\n");
/* We're going to use the ANSI X9.62 Prime 256v1 curve */
if(1 != EVP_PKEY_CTX_set_ec_paramgen_curve_nid(pctx, NID_X9_62_prime256v1))
printf("Error in EC key generation\n");
/* Create the parameter object params */
if (!EVP_PKEY_paramgen(pctx, ¶ms))
printf("Error in EC key generation\n");
/* Create the context for the key generation */
if(NULL == (kctx = EVP_PKEY_CTX_new(params, NULL)))
printf("Error in EC key generation\n");
/* Generate the key */
if(1 != EVP_PKEY_keygen_init(kctx))
printf("Error in EC key generation\n");
if (1 != EVP_PKEY_keygen(kctx, &pkey))
printf("Error in EC key generation\n");
/* Get the peer's public key, and provide the peer with our public key -
* how this is done will be specific to your circumstances */
peerkey = get_peerkey(pkey);
/* Create the context for the shared secret derivation */
if(NULL == (ctx = EVP_PKEY_CTX_new(pkey, NULL)))
printf("Error in EC key generation\n");
/* Initialise */
if(1 != EVP_PKEY_derive_init(ctx))
printf("Error in EC key generation\n");
/* Provide the peer public key */
if(1 != EVP_PKEY_derive_set_peer(ctx, peerkey))
printf("Error in EC key generation\n");
/* Determine buffer length for shared secret */
if(1 != EVP_PKEY_derive(ctx, NULL, secret_len))
printf("Error in EC key generation\n");
/* Create the buffer */
if(NULL == (secret = OPENSSL_malloc(*secret_len)))
printf("Error in EC key generation\n");
/* Derive the shared secret */
if(1 != (EVP_PKEY_derive(ctx, secret, secret_len)))
printf("Error in EC key generation\n");
EVP_PKEY_CTX_free(ctx);
EVP_PKEY_free(peerkey);
EVP_PKEY_free(pkey);
EVP_PKEY_CTX_free(kctx);
EVP_PKEY_free(params);
EVP_PKEY_CTX_free(pctx);
/* Never use a derived secret directly. Typically it is passed
* through some hash function to produce a key */
return secret;
}
我发现为了使此函数起作用,我需要一个带有第二方公钥的EVP_KEY对象。我在一个字节数组中拥有这个公钥,以及它的长度。那么我该如何将其转换为所需的类型?另外我在OpenSSL中找不到secp256r1曲线,但是经过一些研究后,我使用了代码中的曲线。这样做正确吗?
谢谢!