NAME
EVP_DigestVerifyInit,
EVP_DigestVerifyUpdate,
EVP_DigestVerifyFinal,
EVP_DigestVerify —
EVP signature verification
functions
SYNOPSIS
#include
<openssl/evp.h>
int
EVP_DigestVerifyInit(EVP_MD_CTX
*ctx, EVP_PKEY_CTX **pctx, const
EVP_MD *type, ENGINE *engine,
EVP_PKEY *pkey);
int
EVP_DigestVerifyUpdate(EVP_MD_CTX
*ctx, const void *d, size_t
cnt);
int
EVP_DigestVerifyFinal(EVP_MD_CTX
*ctx, const unsigned char *sig,
size_t siglen);
int
EVP_DigestVerify(EVP_MD_CTX
*ctx, const unsigned char *sig,
size_t siglen, const unsigned char
*tbs, size_t *tbslen);
DESCRIPTION
The EVP signature routines are a high-level interface to digital signatures.
EVP_DigestVerifyInit()
sets up the verification context ctx to use the digest
type and the public key pkey.
Before calling this function, obtain ctx from
EVP_MD_CTX_new(3) or call
EVP_MD_CTX_reset(3) on it. The engine
argument is always ignored and passing NULL is
recommended.
If pctx is not NULL,
any pointer passed in as *pctx is ignored and
overwritten by an internal pointer to the EVP_PKEY_CTX
used by the verification operation: this can be used to set alternative
signing options. The returned EVP_PKEY_CTX must not be
freed by the application. It is freed automatically when the
EVP_MD_CTX is freed.
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 siglen.
EVP_DigestVerify()
verifies tbslen bytes at tbs
against the signature in sig of length
siglen. EVP_DigestVerify() is
a one shot operation which verifies a single block of data in one function
call. For algorithms that support streaming it is equivalent to calling
EVP_DigestVerifyUpdate() and
EVP_DigestVerifyFinal().
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.
The call to
EVP_DigestVerifyFinal()
internally finalizes a copy of the digest context. This means that
EVP_VerifyUpdate(3) and
EVP_VerifyFinal(3) 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_free(3) or a memory leak will occur.
RETURN VALUES
EVP_DigestVerifyInit() and
EVP_DigestVerifyUpdate() return 1 for success and 0
for failure.
EVP_DigestVerifyFinal() and
EVP_DigestVerify() return 1 for success; any other
value indicates failure. A return value of 0 indicates that the signature
did not verify successfully (that is, the signature did not match the
original data or the signature had an invalid form), while other values
indicate a more serious error (and sometimes also indicate an invalid
signature form).
The error codes can be obtained from ERR_get_error(3).
SEE ALSO
evp(3), EVP_DigestInit(3), EVP_DigestSignInit(3), EVP_PKEY_meth_set_verifyctx(3)
HISTORY
EVP_DigestVerifyInit(),
EVP_DigestVerifyUpdate(), and
EVP_DigestVerifyFinal() first appeared in OpenSSL
1.0.0 and have been available since OpenBSD 4.9.
EVP_DigestVerify() first appeared in
OpenSSL 1.1.1 and has been available since OpenBSD
7.0.