1=pod 2 3=head1 NAME 4 5EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal - EVP signing 6functions 7 8=head1 SYNOPSIS 9 10 #include <openssl/evp.h> 11 12 int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl); 13 int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt); 14 int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey); 15 16 void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type); 17 18 int EVP_PKEY_size(EVP_PKEY *pkey); 19 20=head1 DESCRIPTION 21 22The EVP signature routines are a high level interface to digital 23signatures. 24 25EVP_SignInit_ex() sets up signing context B<ctx> to use digest 26B<type> from ENGINE B<impl>. B<ctx> must be initialized with 27EVP_MD_CTX_init() before calling this function. 28 29EVP_SignUpdate() hashes B<cnt> bytes of data at B<d> into the 30signature context B<ctx>. This function can be called several times on the 31same B<ctx> to include additional data. 32 33EVP_SignFinal() signs the data in B<ctx> using the private key B<pkey> and 34places the signature in B<sig>. B<sig> must be at least EVP_PKEY_size(pkey) 35bytes in size. B<s> is an OUT paramter, and not used as an IN parameter. 36The number of bytes of data written (i.e. the length of the signature) 37will be written to the integer at B<s>, at most EVP_PKEY_size(pkey) bytes 38will be written. 39 40EVP_SignInit() initializes a signing context B<ctx> to use the default 41implementation of digest B<type>. 42 43EVP_PKEY_size() returns the maximum size of a signature in bytes. The actual 44signature returned by EVP_SignFinal() may be smaller. 45 46=head1 RETURN VALUES 47 48EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1 49for success and 0 for failure. 50 51EVP_PKEY_size() returns the maximum size of a signature in bytes. 52 53The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>. 54 55=head1 NOTES 56 57The B<EVP> interface to digital signatures should almost always be used in 58preference to the low level interfaces. This is because the code then becomes 59transparent to the algorithm used and much more flexible. 60 61Due to the link between message digests and public key algorithms the correct 62digest algorithm must be used with the correct public key type. A list of 63algorithms and associated public key algorithms appears in 64L<EVP_DigestInit(3)|EVP_DigestInit(3)>. 65 66When signing with DSA private keys the random number generator must be seeded 67or the operation will fail. The random number generator does not need to be 68seeded for RSA signatures. 69 70The call to EVP_SignFinal() internally finalizes a copy of the digest context. 71This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called 72later to digest and sign additional data. 73 74Since only a copy of the digest context is ever finalized the context must 75be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak 76will occur. 77 78=head1 BUGS 79 80Older versions of this documentation wrongly stated that calls to 81EVP_SignUpdate() could not be made after calling EVP_SignFinal(). 82 83Since the private key is passed in the call to EVP_SignFinal() any error 84relating to the private key (for example an unsuitable key and digest 85combination) will not be indicated until after potentially large amounts of 86data have been passed through EVP_SignUpdate(). 87 88It is not possible to change the signing parameters using these function. 89 90The previous two bugs are fixed in the newer EVP_SignDigest*() function. 91 92=head1 SEE ALSO 93 94L<EVP_VerifyInit(3)|EVP_VerifyInit(3)>, 95L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>, 96L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>, 97L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>, 98L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)> 99 100=head1 HISTORY 101 102EVP_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are 103available in all versions of SSLeay and OpenSSL. 104 105EVP_SignInit_ex() was added in OpenSSL 0.9.7. 106 107=cut 108