EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal - EVP
signature verification functions
int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t siglen);
The EVP signature routines are a high level interface to digital
EVP_DigestVerifyInit() sets up verification context ctx to use digest
type from ENGINE impl and public key pkey. ctx must be initialized with
EVP_MD_CTX_init() before calling this
function. If pctx is not NULL the EVP_PKEY_CTX of the verification operation will be written
to *pctx: this can be used to set alternative verification options.
EVP_DigestVerifyUpdate() hashes cnt bytes of data at d into the verification context ctx. This function can be called several times on the same ctx to include additional data. This function is currently implemented using a
EVP_DigestVerifyFinal() verifies the data in ctx against the signature in
sig of length siglen.
EVP_DigestVerifyUpdate() return 1 for success and 0 or a
negative value for failure. In particular a return value of -2 indicates
the operation is not supported by the public key algorithm.
Unlike other functions the return value 0 from
EVP_DigestVerifyFinal() only indicates that the signature did
not not verify successfully (that is tbs did not match the original data or
the signature was of invalid form) it is not an indication of a more
The error codes can be obtained from ERR_get_error(3).
The EVP interface to digital signatures should almost always be used in preference
to the low level interfaces. This is because the code then becomes
transparent to the algorithm used and much more flexible.
In previous versions of OpenSSL there was a link between message digest
types and public key algorithms. This meant that ``clone'' digests such as
EVP_dss1() needed to be used to sign using SHA1 and DSA. This
is no longer necessary and the use of clone digest is now discouraged.
For some key types and parameters the random number generator must be
seeded or the operation will fail.
The call to
EVP_DigestVerifyFinal() internally finalizes a
copy of the digest context. This means that calls to
EVP_VerifyFinal() can be
called later to digest and verify additional data.
Since only a copy of the digest context is ever finalized the context must
be cleaned up after use by calling
EVP_MD_CTX_cleanup() or a
memory leak will occur.
evp(3), hmac(3), md2(3),
md5(3), mdc2(3), ripemd(3),
EVP_DigestVerifyFinal() were first added to OpenSSL 1.0.0.