EVP_SIGNINIT(3) OpenSSL EVP_SIGNINIT(3)NAME
EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing
functions
SYNOPSIS
#include <openssl/evp.h>
int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey);
void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
int EVP_PKEY_size(EVP_PKEY *pkey);
DESCRIPTION
The EVP signature routines are a high level interface to
digital signatures.
EVP_SignInit_ex() sets up signing context ctx to use digest
type from ENGINE impl. ctx must be initialized with
EVP_MD_CTX_init() before calling this function.
EVP_SignUpdate() hashes cnt bytes of data at d into the sig-
nature context ctx. This function can be called several
times on the same ctx to include additional data.
EVP_SignFinal() signs the data in ctx using the private key
pkey and places the signature in sig. The number of bytes of
data written (i.e. the length of the signature) will be
written to the integer at s, at most EVP_PKEY_size(pkey)
bytes will be written.
EVP_SignInit() initializes a signing context ctx to use the
default implementation of digest type.
EVP_PKEY_size() returns the maximum size of a signature in
bytes. The actual signature returned by EVP_SignFinal() may
be smaller.
RETURN VALUESEVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal()
return 1 for success and 0 for failure.
EVP_PKEY_size() returns the maximum size of a signature in
bytes.
The error codes can be obtained by 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
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EVP_SIGNINIT(3) OpenSSL EVP_SIGNINIT(3)
because the code then becomes transparent to the algorithm
used and much more flexible.
Due to the link between message digests and public key algo-
rithms the correct digest algorithm must be used with the
correct public key type. A list of algorithms and associated
public key algorithms appears in EVP_DigestInit(3).
When signing with DSA private keys the random number genera-
tor must be seeded or the operation will fail. The random
number generator does not need to be seeded for RSA signa-
tures.
The call to EVP_SignFinal() internally finalizes a copy of
the digest context. This means that calls to
EVP_SignUpdate() and EVP_SignFinal() 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.
BUGS
Older versions of this documentation wrongly stated that
calls to EVP_SignUpdate() could not be made after calling
EVP_SignFinal().
SEE ALSOEVP_VerifyInit(3), EVP_DigestInit(3), ERR_get_error(3),
evp(3), HMAC(3), MD2(3), MD5(3), MDC2(3), RIPEMD(3),
SHA1(3), digest(1)HISTORYEVP_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are
available in all versions of SSLeay and OpenSSL.
EVP_SignInit_ex() was added in OpenSSL 0.9.7.
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