EVP signing functions
*ctx, EVP_PKEY_CTX **pctx, const
EVP_MD *type, ENGINE *e,
*ctx, const void *d, size_t
*ctx, unsigned char *sig, size_t
unsigned char *sigret, size_t
*siglen, const unsigned char *tbs,
The EVP signature routines are a high-level interface to digital signatures.
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
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.
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.
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
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
signs tbslen bytes of data at
tbs and places the signature in
sigret and its length in siglen
in a similar way to
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
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
internally finalizes a copy of the digest context. This means that
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.
EVP_DigestSign() return 1 for success and 0 for
The error codes can be obtained from ERR_get_error(3).
evp(3), EVP_DigestInit(3), EVP_DigestVerifyInit(3), EVP_PKEY_meth_set_signctx(3)
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.