EVP_DigestVerifyInit(3) OpenSSL EVP_DigestVerifyInit(3)
EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal - EVP signature
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 signatures.
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 macro.
EVP_DigestVerifyFinal() verifies the data in ctx against the signature in sig of length
EVP_DigestVerifyInit() and 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 serious error.
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
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_VerifyUpdate() and 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_DigestSignInit(3), EVP_DigestInit(3), err(3), evp(3), hmac(3), md2(3), md5(3),
mdc2(3), ripemd(3), sha(3), dgst(1)
EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal() were first
added to OpenSSL 1.0.0.
1.0.1e 2013-02-11 EVP_DigestVerifyInit(3)