1=pod 2 3=head1 NAME 4 5EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, 6EVP_SignFinal_ex, EVP_SignFinal 7- EVP signing functions 8 9=head1 SYNOPSIS 10 11 #include <openssl/evp.h> 12 13 int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl); 14 int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt); 15 int EVP_SignFinal_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s, 16 EVP_PKEY *pkey, OSSL_LIB_CTX *libctx, const char *propq); 17 int EVP_SignFinal(EVP_MD_CTX *ctx, unsigned char *sig, unsigned int *s, 18 EVP_PKEY *pkey); 19 20 void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type); 21 22=head1 DESCRIPTION 23 24The EVP signature routines are a high-level interface to digital 25signatures. 26 27EVP_SignInit_ex() sets up signing context I<ctx> to use digest 28I<type> from B<ENGINE> I<impl>. I<ctx> must be created with 29EVP_MD_CTX_new() before calling this function. 30 31EVP_SignUpdate() hashes I<cnt> bytes of data at I<d> into the 32signature context I<ctx>. This function can be called several times on the 33same I<ctx> to include additional data. 34 35EVP_SignFinal_ex() signs the data in I<ctx> using the private key 36I<pkey> and places the signature in I<sig>. The library context I<libctx> and 37property query I<propq> are used when creating a context to use with the key 38I<pkey>. I<sig> must be at least C<EVP_PKEY_get_size(pkey)> bytes in size. 39I<s> is an OUT parameter, and not used as an IN parameter. 40The number of bytes of data written (i.e. the length of the signature) 41will be written to the integer at I<s>, at most C<EVP_PKEY_get_size(pkey)> 42bytes will be written. 43 44EVP_SignFinal() is similar to EVP_SignFinal_ex() but uses default 45values of NULL for the library context I<libctx> and the property query I<propq>. 46 47EVP_SignInit() initializes a signing context I<ctx> to use the default 48implementation of digest I<type>. 49 50=head1 RETURN VALUES 51 52EVP_SignInit_ex(), EVP_SignUpdate(), EVP_SignFinal_ex() and 53EVP_SignFinal() return 1 for success and 0 for failure. 54 55The error codes can be obtained by L<ERR_get_error(3)>. 56 57=head1 NOTES 58 59The B<EVP> interface to digital signatures should almost always be used in 60preference to the low-level interfaces. This is because the code then becomes 61transparent to the algorithm used and much more flexible. 62 63When signing with some private key types the random number generator must 64be seeded. If the automatic seeding or reseeding of the OpenSSL CSPRNG fails 65due to external circumstances (see L<RAND(7)>), the operation will fail. 66 67The call to EVP_SignFinal() internally finalizes a copy of the digest context. 68This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called 69later to digest and sign additional data.cApplications may disable this 70behavior by setting the EVP_MD_CTX_FLAG_FINALISE context flag via 71L<EVP_MD_CTX_set_flags(3)>. 72 73Since only a copy of the digest context is ever finalized the context must 74be cleaned up after use by calling EVP_MD_CTX_free() or a memory leak 75will occur. 76 77Note that not all providers support continuation, in case the selected 78provider does not allow to duplicate contexts EVP_SignFinal() will 79finalize the digest context and attempting to process additional data via 80EVP_SignUpdate() will result in an error. 81 82=head1 BUGS 83 84Older versions of this documentation wrongly stated that calls to 85EVP_SignUpdate() could not be made after calling EVP_SignFinal(). 86 87Since the private key is passed in the call to EVP_SignFinal() any error 88relating to the private key (for example an unsuitable key and digest 89combination) will not be indicated until after potentially large amounts of 90data have been passed through EVP_SignUpdate(). 91 92It is not possible to change the signing parameters using these function. 93 94The previous two bugs are fixed in the newer EVP_DigestSign*() functions. 95 96=head1 SEE ALSO 97 98L<EVP_PKEY_get_size(3)>, L<EVP_PKEY_get_bits(3)>, 99L<EVP_PKEY_get_security_bits(3)>, 100L<EVP_VerifyInit(3)>, 101L<EVP_DigestInit(3)>, 102L<evp(7)>, L<HMAC(3)>, L<MD2(3)>, 103L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>, 104L<SHA1(3)>, L<openssl-dgst(1)> 105 106=head1 HISTORY 107 108The function EVP_SignFinal_ex() was added in OpenSSL 3.0. 109 110=head1 COPYRIGHT 111 112Copyright 2000-2023 The OpenSSL Project Authors. All Rights Reserved. 113 114Licensed under the Apache License 2.0 (the "License"). You may not use 115this file except in compliance with the License. You can obtain a copy 116in the file LICENSE in the source distribution or at 117L<https://www.openssl.org/source/license.html>. 118 119=cut 120
