1=pod 2 3=head1 NAME 4 5EVP_SignInit, EVP_SignUpdate, EVP_SignFinal - EVP signing functions 6 7=head1 SYNOPSIS 8 9 #include <openssl/evp.h> 10 11 int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl); 12 int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt); 13 int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey); 14 15 void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type); 16 17 int EVP_PKEY_size(EVP_PKEY *pkey); 18 19=head1 DESCRIPTION 20 21The EVP signature routines are a high level interface to digital 22signatures. 23 24EVP_SignInit_ex() sets up signing context B<ctx> to use digest 25B<type> from ENGINE B<impl>. B<ctx> must be initialized with 26EVP_MD_CTX_init() before calling this function. 27 28EVP_SignUpdate() hashes B<cnt> bytes of data at B<d> into the 29signature context B<ctx>. This function can be called several times on the 30same B<ctx> to include additional data. 31 32EVP_SignFinal() signs the data in B<ctx> using the private key B<pkey> and 33places the signature in B<sig>. B<sig> must be at least EVP_PKEY_size(pkey) 34bytes in size. B<s> is an OUT paramter, and not used as an IN parameter. 35The number of bytes of data written (i.e. the length of the signature) 36will be written to the integer at B<s>, at most EVP_PKEY_size(pkey) bytes 37will be written. 38 39EVP_SignInit() initializes a signing context B<ctx> to use the default 40implementation of digest B<type>. 41 42EVP_PKEY_size() returns the maximum size of a signature in bytes. The actual 43signature returned by EVP_SignFinal() may be smaller. 44 45=head1 RETURN VALUES 46 47EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1 48for success and 0 for failure. 49 50EVP_PKEY_size() returns the maximum size of a signature in bytes. 51 52The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>. 53 54=head1 NOTES 55 56The B<EVP> interface to digital signatures should almost always be used in 57preference to the low level interfaces. This is because the code then becomes 58transparent to the algorithm used and much more flexible. 59 60Due to the link between message digests and public key algorithms the correct 61digest algorithm must be used with the correct public key type. A list of 62algorithms and associated public key algorithms appears in 63L<EVP_DigestInit(3)|EVP_DigestInit(3)>. 64 65When signing with DSA private keys the random number generator must be seeded 66or the operation will fail. The random number generator does not need to be 67seeded for RSA signatures. 68 69The call to EVP_SignFinal() internally finalizes a copy of the digest context. 70This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called 71later to digest and sign additional data. 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_cleanup() or a memory leak 75will occur. 76 77=head1 BUGS 78 79Older versions of this documentation wrongly stated that calls to 80EVP_SignUpdate() could not be made after calling EVP_SignFinal(). 81 82Since the private key is passed in the call to EVP_SignFinal() any error 83relating to the private key (for example an unsuitable key and digest 84combination) will not be indicated until after potentially large amounts of 85data have been passed through EVP_SignUpdate(). 86 87It is not possible to change the signing parameters using these function. 88 89The previous two bugs are fixed in the newer EVP_SignDigest*() function. 90 91=head1 SEE ALSO 92 93L<EVP_VerifyInit(3)|EVP_VerifyInit(3)>, 94L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>, 95L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>, 96L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>, 97L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)> 98 99=head1 HISTORY 100 101EVP_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are 102available in all versions of SSLeay and OpenSSL. 103 104EVP_SignInit_ex() was added in OpenSSL 0.9.7. 105 106=cut 107