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EVP_PKEY_DECRYPT(3)

Library Functions Manual

EVP_PKEY_DECRYPT(3)

NAME

EVP_PKEY_decrypt_init, EVP_PKEY_decrypt —

decrypt using a public key algorithm

SYNOPSIS

#include
  <openssl/evp.h>

int
EVP_PKEY_decrypt_init(EVP_PKEY_CTX *ctx);

int
EVP_PKEY_decrypt(EVP_PKEY_CTX *ctx, unsigned char *out, size_t *outlen, const unsigned char *in, size_t inlen);

DESCRIPTION

The EVP_PKEY_decrypt_init() function initializes a public key algorithm context using key ctx->pkey for a decryption operation.

The EVP_PKEY_decrypt() function performs a public key decryption operation using ctx. The data to be decrypted is specified using the in and inlen parameters. If out is NULL then the maximum size of the output buffer is written to the outlen parameter. If out is not NULL then before the call the outlen parameter should contain the length of the out buffer. If the call is successful, the decrypted data is written to out and the amount of data written to outlen.

After the call to EVP_PKEY_decrypt_init(), algorithm specific control operations can be performed to set any appropriate parameters for the operation.

The function EVP_PKEY_decrypt() can be called more than once on the same context if several operations are performed using the same parameters.

RETURN VALUES

EVP_PKEY_decrypt_init() and EVP_PKEY_decrypt() 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

Decrypt data using OAEP (for RSA keys):

#include <openssl/evp.h> 
#include <openssl/rsa.h> 
 
EVP_PKEY_CTX *ctx; 
ENGINE *eng; 
unsigned char *out, *in; 
size_t outlen, inlen; 
EVP_PKEY *key; 
 
/* 
 * Assumes that key, eng, in, and inlen are already set up 
 * and that key is an RSA private key. 
 */ 
ctx = EVP_PKEY_CTX_new(key, eng); 
if (!ctx) 
	/* Error occurred */ 
if (EVP_PKEY_decrypt_init(ctx) <= 0) 
	/* Error */ 
if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_OAEP_PADDING) <= 0) 
	/* Error */ 
 
/* Determine buffer length */ 
if (EVP_PKEY_decrypt(ctx, NULL, &outlen, in, inlen) <= 0) 
	/* Error */ 
 
out = malloc(outlen); 
 
if (!out) 
	/* malloc failure */ 
 
if (EVP_PKEY_decrypt(ctx, out, &outlen, in, inlen) <= 0) 
	/* Error */ 
 
/* Decrypted data is outlen bytes written to buffer out */

HISTORY

EVP_PKEY_decrypt_init() and EVP_PKEY_decrypt() first appeared in OpenSSL 1.0.0 and have been available since OpenBSD 4.9.

March 31, 2022

Debian