---
name: "libressl-EVP_PKEY_verify_recover"
section: "3"
platform: "linux"
package: "libressl"
version: "4.4.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/libressl-EVP_PKEY_verify_recover"
---

# libressl-EVP\_PKEY\_verify\_recover(3)

recover signature using a public key algorithm

## NAME

**EVP\_PKEY\_verify\_recover\_init**, **EVP\_PKEY\_verify\_recover** – recover signature using a public key algorithm

## SYNOPSIS

Crypto Library (libcrypto, -lcrypto)

**#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*);

## DESCRIPTION

The **EVP\_PKEY\_verify\_recover\_init**() function initializes a public key algorithm context using key *ctx-\>pkey* for a verify recover operation.

The **EVP\_PKEY\_verify\_recover**() function recovers signed data using *ctx*. The signature is specified using the *sig* and *siglen* parameters. If *rout* is NULL, then the maximum size of the output buffer is written to the *routlen* parameter. If *rout* is not NULL, then before the call the *routlen* parameter should contain the length of the *rout* buffer. If the call is successful, recovered data is written to *rout* and the amount of data written to *routlen*.

Normally an application is only interested in whether a signature verification operation is successful. In those cases, the EVP\_PKEY\_verify(3) 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.

## 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.

## EXAMPLES

Recover digest originally signed using PKCS#1 and SHA-256 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;
/*
 * Assumes that 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, NULL);
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 */
```

## SEE ALSO

EVP\_PKEY\_CTX\_new(3), EVP\_PKEY\_decrypt(3), EVP\_PKEY\_derive(3), EVP\_PKEY\_encrypt(3), EVP\_PKEY\_sign(3), EVP\_PKEY\_verify(3)

## HISTORY

**EVP\_PKEY\_verify\_recover\_init**() and **EVP\_PKEY\_verify\_recover**() first appeared in OpenSSL 1.0.0 and have been available since OpenBSD 4.9.