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, size_t cnt);
int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, const 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 VALUES¶
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.
EVP_DigestVerifyFinal() returns 1 for success; any other value indicates
failure. A return value of zero indicates that the signature did not verify
successfully (that is, tbs 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).
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
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 ALSO¶
EVP_DigestSignInit(3),
EVP_DigestInit(3),
err(3),
evp(3),
hmac(3),
md2(3),
md5(3),
mdc2(3),
ripemd(3),
sha(3),
dgst(1)
HISTORY¶
EVP_DigestVerifyInit(),
EVP_DigestVerifyUpdate() and
EVP_DigestVerifyFinal() were first added to OpenSSL 1.0.0.