EVP_DigestVerifyInit(3) OpenSSL EVP_DigestVerifyInit(3)NAME
EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal -
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 *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);
DESCRIPTION
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 siglen.
RETURN VALUESEVP_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).
NOTES
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_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.
SEE ALSOEVP_DigestSignInit(3), EVP_DigestInit(3), err(3), evp(3), hmac(3),
md2(3), md5(3), mdc2(3), ripemd(3), sha(3), dgst(1)HISTORYEVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and
EVP_DigestVerifyFinal() were first added to OpenSSL 1.0.0.
1.0.1e 2013-02-11 EVP_DigestVerifyInit(3)
