NAME
EVP_DigestSignInit,
EVP_DigestSignUpdate,
EVP_DigestSignFinal,
EVP_DigestSign —
EVP signing functions
SYNOPSIS
#include
<openssl/evp.h>
int
EVP_DigestSignInit(EVP_MD_CTX
*ctx, EVP_PKEY_CTX **pctx, const
EVP_MD *type, ENGINE *engine,
EVP_PKEY *pkey);
int
EVP_DigestSignUpdate(EVP_MD_CTX
*ctx, const void *d, size_t
cnt);
int
EVP_DigestSignFinal(EVP_MD_CTX
*ctx, unsigned char *sig, size_t
*siglen);
int
EVP_DigestSign(EVP_MD_CTX *ctx,
unsigned char *sigret, size_t
*siglen, const unsigned char *tbs,
size_t tbslen);
DESCRIPTION
The EVP signature routines are a high-level interface to digital signatures.
EVP_DigestSignInit()
sets up the signing context ctx to use the digest
type and the private 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 signing 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_DigestSignUpdate()
hashes cnt bytes of data at d
into the signature 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_DigestSignFinal()
signs the data in ctx and places the signature in
sig. If sig is
NULL, then the maximum size of the output buffer is
written to *siglen. If sig is
not NULL, then before the call
siglen should contain the length of the
sig buffer. If the call is successful, the signature
is written to sig and the amount of data written to
siglen.
EVP_DigestSign()
signs tbslen bytes of data at
tbs and places the signature in
sigret and its length in siglen
in a similar way to EVP_DigestSignFinal().
EVP_DigestSign() is a one shot operation which signs
a single block of data with one function call. For algorithms that support
streaming it is equivalent to calling
EVP_DigestSignUpdate() and
EVP_DigestSignFinal().
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_DigestSignFinal()
internally finalizes a copy of the digest context. This means that
EVP_DigestSignUpdate() and
EVP_DigestSignFinal() can be called later to digest
and sign 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.
The use of EVP_PKEY_size(3) with these functions is discouraged because some signature operations may have a signature length which depends on the parameters set. As a result, EVP_PKEY_size(3) would have to return a value which indicates the maximum possible signature for any set of parameters.
RETURN VALUES
EVP_DigestSignInit(),
EVP_DigestSignUpdate(),
EVP_DigestSignFinal(), and
EVP_DigestSign() return 1 for success and 0 for
failure.
The error codes can be obtained from ERR_get_error(3).
SEE ALSO
evp(3), EVP_DigestInit(3), EVP_DigestVerifyInit(3), EVP_PKEY_meth_set_signctx(3)
HISTORY
EVP_DigestSignInit(),
EVP_DigestSignUpdate(), and
EVP_DigestSignFinal() first appeared in OpenSSL
1.0.0 and have been available since OpenBSD 4.9.
EVP_DigestSign() first appeared in OpenSSL
1.1.1 and has been available since OpenBSD 7.0.