.\" $OpenBSD: EVP_SignInit.3,v 1.16 2022/07/13 19:10:40 schwarze Exp $ .\" full merge up to: OpenSSL b97fdb57 Nov 11 09:33:09 2016 +0100 .\" selective merge up to: OpenSSL 79b49fb0 Mar 20 10:03:10 2018 +1000 .\" .\" This file was written by Dr. Stephen Henson . .\" Copyright (c) 2000-2002, 2005, 2006, 2014-2016 The OpenSSL Project. .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in .\" the documentation and/or other materials provided with the .\" distribution. .\" .\" 3. 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IN NO EVENT SHALL THE OpenSSL PROJECT OR .\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, .\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, .\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED .\" OF THE POSSIBILITY OF SUCH DAMAGE. .\" .Dd $Mdocdate: July 13 2022 $ .Dt EVP_SIGNINIT 3 .Os .Sh NAME .Nm EVP_SignInit_ex , .Nm EVP_SignUpdate , .Nm EVP_SignFinal , .Nm EVP_SignInit .Nd EVP signing functions .Sh SYNOPSIS .In openssl/evp.h .Ft int .Fo EVP_SignInit_ex .Fa "EVP_MD_CTX *ctx" .Fa "const EVP_MD *type" .Fa "ENGINE *impl" .Fc .Ft int .Fo EVP_SignUpdate .Fa "EVP_MD_CTX *ctx" .Fa "const void *d" .Fa "unsigned int cnt" .Fc .Ft int .Fo EVP_SignFinal .Fa "EVP_MD_CTX *ctx" .Fa "unsigned char *sig" .Fa "unsigned int *s" .Fa "EVP_PKEY *pkey" .Fc .Ft void .Fo EVP_SignInit .Fa "EVP_MD_CTX *ctx" .Fa "const EVP_MD *type" .Fc .Sh DESCRIPTION The EVP signature routines are a high level interface to digital signatures. .Pp .Fn EVP_SignInit_ex sets up a signing context .Fa ctx to use the digest .Fa type from .Vt ENGINE .Fa impl . .Fa ctx must be initialized with .Xr EVP_MD_CTX_init 3 before calling this function. .Pp .Fn EVP_SignUpdate hashes .Fa cnt bytes of data at .Fa d into the signature context .Fa ctx . This function can be called several times on the same .Fa ctx to include additional data. .Pp .Fn EVP_SignFinal signs the data in .Fa ctx using the private key .Fa pkey and places the signature in .Fa sig . .Fa sig must be at least .Xr EVP_PKEY_size 3 bytes in size. .Fa 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 .Fa s . At most .Xr EVP_PKEY_size 3 bytes will be written. .Pp .Fn EVP_SignInit initializes a signing context .Fa ctx to use the default implementation of digest .Fa type . .Pp 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. .Pp The call to .Fn EVP_SignFinal internally finalizes a copy of the digest context. This means that calls to .Fn EVP_SignUpdate and .Fn EVP_SignFinal can be called later to digest and sign additional data. .Pp Since only a copy of the digest context is ever finalized, the context must be cleaned up after use by calling .Xr EVP_MD_CTX_free 3 or a memory leak will occur. .Sh RETURN VALUES .Fn EVP_SignInit_ex , .Fn EVP_SignUpdate , and .Fn EVP_SignFinal return 1 for success and 0 for failure. .Pp The error codes can be obtained by .Xr ERR_get_error 3 . .Sh SEE ALSO .Xr evp 3 , .Xr EVP_DigestInit 3 , .Xr EVP_PKEY_asn1_set_public 3 , .Xr EVP_PKEY_size 3 , .Xr EVP_VerifyInit 3 .Sh HISTORY .Fn EVP_SignInit , .Fn EVP_SignUpdate , and .Fn EVP_SignFinal first appeared in SSLeay 0.5.1 and have been available since .Ox 2.4 . .Pp .Fn EVP_SignInit_ex first appeared in OpenSSL 0.9.7 and has been available since .Ox 3.2 . .Sh BUGS Older versions of this documentation wrongly stated that calls to .Fn EVP_SignUpdate could not be made after calling .Fn EVP_SignFinal . .Pp Since the private key is passed in the call to .Fn 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 .Fn EVP_SignUpdate . .Pp It is not possible to change the signing parameters using these function. .Pp The previous two bugs are fixed in the newer EVP_DigestSign* function.