EVP_DIGESTSIGNINIT(3SSL) OpenSSL EVP_DIGESTSIGNINIT(3SSL)
NAME
EVP_DigestSignInit_ex, EVP_DigestSignInit, EVP_DigestSignUpdate,
EVP_DigestSignFinal, EVP_DigestSign - EVP signing functions
SYNOPSIS
#include <openssl/evp.h>
int EVP_DigestSignInit_ex(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
const char *mdname, OSSL_LIB_CTX *libctx,
const char *props, EVP_PKEY *pkey,
const OSSL_PARAM params[]);
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, size_t cnt);
int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);
int EVP_DigestSign(EVP_MD_CTX *ctx, unsigned char *sig,
size_t *siglen, const unsigned char *tbs,
size_t tbslen);
DESCRIPTION
The EVP signature routines are a high-level interface to digital
signatures. Input data is digested first before the signing takes
place.
EVP_DigestSignInit_ex() sets up signing context ctx to use a digest with
the name mdname and private key pkey. The name of the digest to be used
is passed to the provider of the signature algorithm in use. How that
provider interprets the digest name is provider specific. The provider
may implement that digest directly itself or it may (optionally) choose
to fetch it (which could result in a digest from a different provider
being selected). If the provider supports fetching the digest then it
may use the props argument for the properties to be used during the
fetch. Finally, the passed parameters params, if not NULL, are set on
the context before returning.
The pkey algorithm is used to fetch a EVP_SIGNATURE method implicitly,
to be used for the actual signing. See "Implicit fetch" in provider(7)
for more information about implicit fetches.
The OpenSSL default and legacy providers support fetching digests and
can fetch those digests from any available provider. The OpenSSL FIPS
provider also supports fetching digests but will only fetch digests that
are themselves implemented inside the FIPS provider.
ctx must be created with EVP_MD_CTX_new() 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.
Note that any existing value in *pctx is overwritten. The EVP_PKEY_CTX
value returned must not be freed directly by the application if ctx is
not assigned an EVP_PKEY_CTX value before being passed to
EVP_DigestSignInit_ex() (which means the EVP_PKEY_CTX is created inside
EVP_DigestSignInit_ex() and it will be freed automatically when the
EVP_MD_CTX is freed). If the EVP_PKEY_CTX to be used is created by
EVP_DigestSignInit_ex then it will use the OSSL_LIB_CTX specified in
libctx and the property query string specified in props.
The digest mdname may be NULL if the signing algorithm supports it. The
props argument can always be NULL.
No EVP_PKEY_CTX will be created by EVP_DigestSignInit_ex() if the passed
ctx has already been assigned one via EVP_MD_CTX_set_pkey_ctx(3). See
also SM2(7).
Only EVP_PKEY types that support signing can be used with these
functions. This includes MAC algorithms where the MAC generation is
considered as a form of "signing". Built-in EVP_PKEY types supported by
these functions are CMAC, Poly1305, DSA, ECDSA, HMAC, RSA, SipHash,
Ed25519 and Ed448.
Not all digests can be used for all key types. The following
combinations apply.
DSA Supports SHA1, SHA224, SHA256, SHA384 and SHA512
ECDSA
Supports SHA1, SHA224, SHA256, SHA384, SHA512 and SM3
RSA with no padding
Supports no digests (the digest type must be NULL)
RSA with X931 padding
Supports SHA1, SHA256, SHA384 and SHA512
All other RSA padding types
Support SHA1, SHA224, SHA256, SHA384, SHA512, MD5, MD5_SHA1, MD2,
MD4, MDC2, SHA3-224, SHA3-256, SHA3-384, SHA3-512
Ed25519 and Ed448
Support no digests (the digest type must be NULL)
HMAC
Supports any digest
CMAC, Poly1305 and SipHash
Will ignore any digest provided.
If RSA-PSS is used and restrictions apply then the digest must match.
EVP_DigestSignInit() works in the same way as EVP_DigestSignInit_ex()
except that the mdname parameter will be inferred from the supplied
digest type, and props will be NULL. Where supplied the ENGINE e will be
used for the signing and digest algorithm implementations. e may be
NULL.
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. ctx MUST NOT be NULL.
Unless sig is NULL EVP_DigestSignFinal() signs the data in ctx and
places the signature in sig. Otherwise the maximum necessary 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_DigestSign() is similar to a single call to EVP_DigestSignUpdate()
and EVP_DigestSignFinal(). Unless sig is NULL, EVP_DigestSign() signs
the data tbs of length tbslen bytes and places the signature in a buffer
sig of size siglen. If sig is NULL, the maximum necessary size of the
signature buffer is written to the siglen parameter.
RETURN VALUES
EVP_DigestSignInit(), EVP_DigestSignUpdate(), EVP_DigestSignFinal() and
EVP_DigestSign() return 1 for success and 0 for failure.
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.
EVP_DigestSign() is a one shot operation which signs a single block of
data in one function. For algorithms that support streaming it is
equivalent to calling EVP_DigestSignUpdate() and EVP_DigestSignFinal().
For algorithms which do not support streaming (e.g. PureEdDSA) it is the
only way to sign data.
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. 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_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. Applications may disable this behavior by setting the
EVP_MD_CTX_FLAG_FINALISE context flag via EVP_MD_CTX_set_flags(3).
Note that not all providers support continuation, in case the selected
provider does not allow to duplicate contexts EVP_DigestSignFinal() will
finalize the digest context and attempting to process additional data
via EVP_DigestSignUpdate() will result in an error.
EVP_DigestSignInit() and EVP_DigestSignInit_ex() functions can be called
multiple times on a context and the parameters set by previous calls
should be preserved if the pkey parameter is NULL. The call then just
resets the state of the ctx.
EVP_DigestSign() can not be called again, once a signature is generated
(by passing sig as non NULL), unless the EVP_MD_CTX is reinitialised by
calling EVP_DigestSignInit_ex().
Ignoring failure returns of EVP_DigestSignInit() and
EVP_DigestSignInit_ex() functions can lead to subsequent undefined
behavior when calling EVP_DigestSignUpdate(), EVP_DigestSignFinal(), or
EVP_DigestSign().
The use of EVP_PKEY_get_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_get_size() would
have to return a value which indicates the maximum possible signature
for any set of parameters.
SEE ALSO
EVP_DigestVerifyInit(3), EVP_DigestInit(3), evp(7), HMAC(3), MD2(3),
MD5(3), MDC2(3), RIPEMD160(3), SHA1(3), openssl-dgst(1), RAND(7)
HISTORY
EVP_DigestSignInit(), EVP_DigestSignUpdate() and EVP_DigestSignFinal()
were added in OpenSSL 1.0.0.
EVP_DigestSignInit_ex() was added in OpenSSL 3.0.
EVP_DigestSignUpdate() was converted from a macro to a function in
OpenSSL 3.0.
COPYRIGHT
Copyright 2006-2024 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>.
3.5.7 2026-06-09 EVP_DIGESTSIGNINIT(3SSL)
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