1 files changed, 131 insertions, 0 deletions

diff --git a/src/lib/libcrypto/man/EVP_PKEY_verify_recover.3 b/src/lib/libcrypto/man/EVP_PKEY_verify_recover.3
new file mode 100644
index 0000000000..fc26152ae6
--- /dev/null
+++ b/src/lib/libcrypto/man/EVP_PKEY_verify_recover.3
@@ -0,0 +1,131 @@
+.Dd $Mdocdate: November 3 2016 $
+.Dt EVP_PKEY_VERIFY_RECOVER 3
+.Os
+.Sh NAME
+.Nm EVP_PKEY_verify_recover_init ,
+.Nm EVP_PKEY_verify_recover
+.Nd recover signature using a public key algorithm
+.Sh SYNOPSIS
+.In openssl/evp.h
+.Ft int
+.Fo EVP_PKEY_verify_recover_init
+.Fa "EVP_PKEY_CTX *ctx"
+.Fc
+.Ft int
+.Fo EVP_PKEY_verify_recover
+.Fa "EVP_PKEY_CTX *ctx"
+.Fa "unsigned char *rout"
+.Fa "size_t *routlen"
+.Fa "const unsigned char *sig"
+.Fa "size_t siglen"
+.Fc
+.Sh DESCRIPTION
+The
+.Fn EVP_PKEY_verify_recover_init
+function initializes a public key algorithm context using key
+.Fa ctx->pkey
+for a verify recover operation.
+.Pp
+The
+.Fn EVP_PKEY_verify_recover
+function recovers signed data using
+.Fa ctx .
+The signature is specified using the
+.Fa sig
+and
+.Fa siglen
+parameters.
+If
+.Fa rout
+is
+.Dv NULL ,
+then the maximum size of the output buffer is written to the
+.Fa routlen
+parameter.
+If
+.Fa rout
+is not
+.Dv NULL ,
+then before the call the
+.Fa routlen
+parameter should contain the length of the
+.Fa rout
+buffer.
+If the call is successful, recovered data is written to
+.Fa rout
+and the amount of data written to
+.Fa routlen .
+.Pp
+Normally an application is only interested in whether a signature
+verification operation is successful.
+In those cases, the
+.Xr EVP_verify 3
+function should be used.
+.Pp
+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).
+.Pp
+After the call to
+.Fn EVP_PKEY_verify_recover_init ,
+algorithm specific control operations can be performed to set any
+appropriate parameters for the operation.
+.Pp
+The function
+.Fn EVP_PKEY_verify_recover
+can be called more than once on the same context if several operations
+are performed using the same parameters.
+.Sh RETURN VALUES
+.Fn EVP_PKEY_verify_recover_init
+and
+.Fn 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.
+.Sh EXAMPLES
+Recover digest originally signed using PKCS#1 and SHA256 digest:
+.Bd -literal
+#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 = 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 */
+.Ed
+.Sh SEE ALSO
+.Xr EVP_PKEY_CTX_new 3 ,
+.Xr EVP_PKEY_encrypt 3 ,
+.Xr EVP_PKEY_decrypt 3 ,
+.Xr EVP_PKEY_sign 3 ,
+.Xr EVP_PKEY_verify 3 ,
+.Xr EVP_PKEY_derive 3
+.Sh HISTORY
+These functions were first added to OpenSSL 1.0.0.