#use wml::openssl-macros area=docs page=EVP_DigestSignInit
EVP_DigestSignInit, EVP_DigestSignUpdate, EVP_DigestSignFinal - EVP signing functions
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);
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
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.
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).
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
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.
EVP_DigestVerifyInit(3), EVP_DigestInit(3), err(3), evp(3), hmac(3), md2(3), md5(3), mdc2(3), ripemd(3), sha(3), dgst(1)
EVP_DigestSignFinal() were first added to OpenSSL 1.0.0.