| =pod |
| |
| =head1 NAME |
| |
| EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal |
| - EVP signing functions |
| |
| =head1 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); |
| |
| =head1 DESCRIPTION |
| |
| The EVP signature routines are a high level interface to digital |
| signatures. |
| |
| EVP_SignInit_ex() sets up signing context I<ctx> to use digest |
| I<type> from B<ENGINE> I<impl>. I<ctx> must be created with |
| EVP_MD_CTX_new() before calling this function. |
| |
| EVP_SignUpdate() hashes I<cnt> bytes of data at I<d> into the |
| signature context I<ctx>. This function can be called several times on the |
| same I<ctx> to include additional data. |
| |
| EVP_SignFinal() signs the data in I<ctx> using the private key I<pkey> and |
| places the signature in I<sig>. I<sig> must be at least C<EVP_PKEY_size(pkey)> |
| bytes in size. I<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 I<s>, at most C<EVP_PKEY_size(pkey)> bytes |
| will be written. |
| |
| EVP_SignInit() initializes a signing context I<ctx> to use the default |
| implementation of digest I<type>. |
| |
| =head1 RETURN VALUES |
| |
| EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1 |
| for success and 0 for failure. |
| |
| The error codes can be obtained by L<ERR_get_error(3)>. |
| |
| =head1 NOTES |
| |
| The B<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 DSA private keys the random number generator must be seeded. |
| If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to |
| external circumstances (see L<RAND(7)>), the operation will fail. |
| This requirement does not hold for RSA signatures. |
| |
| 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_free() or a memory leak |
| will occur. |
| |
| =head1 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_SignDigest*() function. |
| |
| =head1 SEE ALSO |
| |
| L<EVP_PKEY_size(3)>, L<EVP_PKEY_bits(3)>, L<EVP_PKEY_security_bits(3)>, |
| L<EVP_VerifyInit(3)>, |
| L<EVP_DigestInit(3)>, |
| L<evp(7)>, L<HMAC(3)>, L<MD2(3)>, |
| L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>, |
| L<SHA1(3)>, L<openssl-dgst(1)> |
| |
| =head1 COPYRIGHT |
| |
| Copyright 2000-2020 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 |
| L<https://www.openssl.org/source/license.html>. |
| |
| =cut |
