Commit d64c533a authored by Emilia Kasper's avatar Emilia Kasper
Browse files

Improve EVP_PKEY_sign documentation 



Clarify the intended use of EVP_PKEY_sign. Make the code example compile.

Reviewed-by: default avatarDr Stephen Henson <steve@openssl.org>
parent a520ae36

doc/crypto/EVP_PKEY_sign.pod

+15 −5
Original line number Diff line number Diff line
@@ -28,9 +28,14 @@ B<sig> and the amount of data written to B<siglen>. 


=head1 NOTES



EVP_PKEY_sign() does not hash the data to be signed, and therefore is

normally used to sign digests. For signing arbitrary messages, see the

L<EVP_DigestSignInit(3)|EVP_DigestSignInit(3)> and

L<EVP_SignInit(3)|EVP_SignInit(3)> signing interfaces instead.



After the call to EVP_PKEY_sign_init() algorithm specific control

operations can be performed to set any appropriate parameters for the

operation.

operation (see L<EVP_PKEY_CTX_ctrl(3)|EVP_PKEY_CTX_ctrl(3)>).



The function EVP_PKEY_sign() can be called more than once on the same

context if several operations are performed using the same parameters.
@@ -49,13 +54,17 @@ Sign data using RSA with PKCS#1 padding and SHA256 digest: 
 #include <openssl/rsa.h>



 EVP_PKEY_CTX *ctx;

 /* md is a SHA-256 digest in this example. */

 unsigned char *md, *sig;

 size_t mdlen, siglen; 

 size_t mdlen = 32, siglen;

 EVP_PKEY *signing_key;

 /* NB: assumes signing_key, md and mdlen are already set up

  * and that signing_key is an RSA private key



 /*

  * NB: assumes signing_key and md are set up before the next

  * step. signing_key must be an RSA private key and md must

  * point to the SHA-256 digest to be signed.

  */

 ctx = EVP_PKEY_CTX_new(signing_key);

 ctx = EVP_PKEY_CTX_new(signing_key, NULL /* no engine */);

 if (!ctx)

	/* Error occurred */

 if (EVP_PKEY_sign_init(ctx) <= 0)
@@ -83,6 +92,7 @@ Sign data using RSA with PKCS#1 padding and SHA256 digest: 
=head1 SEE ALSO



L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>,

L<EVP_PKEY_CTX_ctrl(3)|EVP_PKEY_CTX_ctrl(3)>,

L<EVP_PKEY_encrypt(3)|EVP_PKEY_encrypt(3)>,

L<EVP_PKEY_decrypt(3)|EVP_PKEY_decrypt(3)>,

L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>,