Initial Commit

openssl-1.0.2f/doc/crypto/EVP_PKEY_verify_recover.pod

@@ -0,0 +1,103 @@
+=pod
+
+=head1 NAME
+
+EVP_PKEY_verify_recover_init, EVP_PKEY_verify_recover - recover signature using a public key algorithm
+
+=head1 SYNOPSIS
+
+ #include <openssl/evp.h>
+
+ int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx);
+ int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx,
+			unsigned char *rout, size_t *routlen,
+			const unsigned char *sig, size_t siglen);
+
+=head1 DESCRIPTION
+
+The EVP_PKEY_verify_recover_init() function initializes a public key algorithm
+context using key B<pkey> for a verify recover operation.
+
+The EVP_PKEY_verify_recover() function recovers signed data
+using B<ctx>. The signature is specified using the B<sig> and
+B<siglen> parameters. If B<rout> is B<NULL> then the maximum size of the output
+buffer is written to the B<routlen> parameter. If B<rout> is not B<NULL> then
+before the call the B<routlen> parameter should contain the length of the
+B<rout> buffer, if the call is successful recovered data is written to
+B<rout> and the amount of data written to B<routlen>.
+
+=head1 NOTES
+
+Normally an application is only interested in whether a signature verification
+operation is successful in those cases the EVP_verify() function should be 
+used.
+
+Sometimes however it is useful to obtain the data originally signed using a
+signing operation. Only certain public key algorithms can recover a signature
+in this way (for example RSA in PKCS padding mode).
+
+After the call to EVP_PKEY_verify_recover_init() algorithm specific control
+operations can be performed to set any appropriate parameters for the
+operation.
+
+The function EVP_PKEY_verify_recover() can be called more than once on the same
+context if several operations are performed using the same parameters.
+
+=head1 RETURN VALUES
+
+EVP_PKEY_verify_recover_init() and EVP_PKEY_verify_recover() return 1 for success
+and 0 or a negative value for failure. In particular a return value of -2
+indicates the operation is not supported by the public key algorithm.
+
+=head1 EXAMPLE
+
+Recover digest originally signed using PKCS#1 and SHA256 digest:
+
+ #include <openssl/evp.h>
+ #include <openssl/rsa.h>
+
+ EVP_PKEY_CTX *ctx;
+ unsigned char *rout, *sig;
+ size_t routlen, siglen; 
+ EVP_PKEY *verify_key;
+ /* NB: assumes verify_key, sig and siglen are already set up
+  * and that verify_key is an RSA public key
+  */
+ ctx = EVP_PKEY_CTX_new(verify_key);
+ if (!ctx)
+	/* Error occurred */
+ if (EVP_PKEY_verify_recover_init(ctx) <= 0)
+	/* Error */
+ if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
+	/* Error */
+ if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
+	/* Error */
+
+ /* Determine buffer length */
+ if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0)
+	/* Error */
+
+ rout = OPENSSL_malloc(routlen);
+
+ if (!rout)
+	/* malloc failure */
+ 
+ if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0)
+	/* Error */
+
+ /* Recovered data is routlen bytes written to buffer rout */
+
+=head1 SEE ALSO
+
+L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>,
+L<EVP_PKEY_encrypt(3)|EVP_PKEY_encrypt(3)>,
+L<EVP_PKEY_decrypt(3)|EVP_PKEY_decrypt(3)>,
+L<EVP_PKEY_sign(3)|EVP_PKEY_sign(3)>,
+L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>,
+L<EVP_PKEY_derive(3)|EVP_PKEY_derive(3)> 
+
+=head1 HISTORY
+
+These functions were first added to OpenSSL 1.0.0.
+
+=cut