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EVP_DIGESTSIGNINIT(3) | Library Functions Manual | EVP_DIGESTSIGNINIT(3) |
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 *e,
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 from
ENGINE e and
private key pkey.
ctx must be initialized with
EVP_MD_CTX_init(3)
before calling this function. If pctx is not
NULL
, the
EVP_PKEY_CTX of the signing operation will be
written to *pctx: this can be used to set
alternative signing options. Any existing value in
*pctx will be overwritten. The
EVP_PKEY_CTX value returned must not be freed
directly by the application. It will be 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.
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(3) needed
to be used to sign using SHA1 and DSA. This is no longer necessary and the use
of clone digest is now discouraged.
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.May 20, 2021 | Debian |