EVP_SIGNINIT(3ossl) OpenSSL EVP_SIGNINIT(3ossl)
NAME
EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal_ex,
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_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s,
EVP_PKEY *pkey, OSSL_LIB_CTX *libctx, const char *propq);
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);
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 created with EVP_MD_CTX_new() before calling
this function.
EVP_SignUpdate() 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.
EVP_SignFinal_ex() signs the data in ctx using the private key pkey and
places the signature in sig. The library context libctx and property
query propq are used when creating a context to use with the key pkey.
sig must be at least "EVP_PKEY_get_size(pkey)" bytes in size. s is an
OUT parameter, and not used as an IN parameter. 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_get_size(pkey)" bytes will be written.
EVP_SignFinal() is similar to EVP_SignFinal_ex() but uses default
values of NULL for the library context libctx and the property query
propq.
EVP_SignInit(3) initializes a signing context ctx to use the default
implementation of digest type.
RETURN VALUES
EVP_SignInit_ex(), EVP_SignUpdate(), EVP_SignFinal_ex() and
EVP_SignFinal() return 1 for success and 0 for failure.
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 because the code then
becomes transparent to the algorithm used and much more flexible.
When signing with some private key types the random number generator
must be seeded. If the automatic seeding or reseeding of the OpenSSL
CSPRNG fails due to external circumstances (see RAND(7)), the operation
will fail.
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.cApplications
may disable this behavior by setting the EVP_MD_CTX_FLAG_FINALISE
context flag via EVP_MD_CTX_set_flags(3).
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() or a memory
leak will occur.
Note that not all providers support continuation, in case the selected
provider does not allow to duplicate contexts EVP_SignFinal() will
finalize the digest context and attempting to process additional data
via EVP_SignUpdate() will result in an error.
BUGS
Older versions of this documentation wrongly stated that calls to
EVP_SignUpdate() could not be made after calling EVP_SignFinal().
Since the private key is passed in the call to EVP_SignFinal() any
error relating to the private key (for example an unsuitable key and
digest combination) will not be indicated until after potentially large
amounts of data have been passed through EVP_SignUpdate().
It is not possible to change the signing parameters using these
function.
The previous two bugs are fixed in the newer EVP_DigestSign*()
functions.
SEE ALSO
EVP_PKEY_get_size(3), EVP_PKEY_get_bits(3),
EVP_PKEY_get_security_bits(3), EVP_VerifyInit(3), EVP_DigestInit(3),
evp(7), HMAC(3), MD2(3), MD5(3), MDC2(3), RIPEMD160(3), SHA1(3),
openssl-dgst(1)
HISTORY
The function EVP_SignFinal_ex() was added in OpenSSL 3.0.
COPYRIGHT
Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.4.0 2024-10-29 EVP_SIGNINIT(3ossl)
openssl 3.4.0 - Generated Thu Nov 7 14:32:48 CST 2024