EVP_DigestSignInit(3) OpenSSL EVP_DigestSignInit(3)NAME
EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal - 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, unsigned int cnt);
int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);
DESCRIPTION
The EVP signature routines are a high level interface to digital
signatures.
EVP_DigestSignInit() sets up signing context ctx to use digest type
from ENGINE impl and private 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 signing operation will be written to *pctx: this
can be used to set alternative signing options.
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 usig
a macro.
EVP_DigestSignFinal() signs the data in ctx places the signature in
sig. If sig is NULL then the maximum size of the output buffer is
written to the siglen parameter. If sig is not NULL then before the
call the siglen parameter 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.
RETURN VALUESEVP_DigestSignInit()EVP_DigestSignUpdate() and EVP_DigestSignaFinal()
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.
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_DigestSignFinal() internally finalizes a copy of the
digest context. This means that calls to 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_cleanup() or a
memory leak will occur.
The use of EVP_PKEY_size() 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() would have to return a
value which indicates the maximum possible signature for any set of
parameters.
SEE ALSOEVP_DigestVerifyInit(3), EVP_DigestInit(3), err(3), evp(3), hmac(3),
md2(3), md5(3), mdc2(3), ripemd(3), sha(3), dgst(1)HISTORYEVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal()
were first added to OpenSSL 1.0.0.
1.0.0k 2013-02-05 EVP_DigestSignInit(3)
