evp(3) OpenSSL evp(3)

## NAME

evp - high-level cryptographic functions

## SYNOPSIS

#include <openssl/evp.h>

## DESCRIPTION

The EVP library provides a high-level interface to cryptographic functions.EVP_Seal...andEVP_Open...provide public key encryption and decryption to implement digital "envelopes". TheEVP_DigestSign...andEVP_DigestVerify...functions implement digital signatures and Message Authentication Codes (MACs). Also see the olderEVP_Sign...andEVP_Verify...functions. Symmetric encryption is available with theEVP_Encrypt...functions. TheEVP_Digest...functions provide message digests. TheEVP_PKEY...functions provide a high level interface to asymmetric algorithms. To create a new EVP_PKEY seeEVP_PKEY_new(3). EVP_PKEYs can be associated with a private key of a particular algorithm by using the functions described on theEVP_PKEY_set1_RSA(3)page, or new keys can be generated usingEVP_PKEY_keygen(3). EVP_PKEYs can be compared usingEVP_PKEY_cmp(3), or printed usingEVP_PKEY_print_private(3). The EVP_PKEY functions support the full range of asymmetric algorithm operations: For key agreement seeEVP_PKEY_derive(3)For signing and verifying seeEVP_PKEY_sign(3),EVP_PKEY_verify(3)andEVP_PKEY_verify_recover(3). However, note that these functions do not perform a digest of the data to be signed. Therefore normally you would use theEVP_DigestSign...functions for this purpose. For encryption and decryption seeEVP_PKEY_encrypt(3)andEVP_PKEY_decrypt(3)respectively. However, note that these functions perform encryption and decryption only. As public key encryption is an expensive operation, normally you would wrap an encrypted message in a "digital envelope" using theEVP_Seal...andEVP_Open...functions. TheEVP_BytesToKey(3)function provides some limited support for password based encryption. Careful selection of the parameters will provide a PKCS#5 PBKDF1 compatible implementation. However, new applications should not typically use this (preferring, for example, PBKDF2 from PCKS#5). Algorithms are loaded withOpenSSL_add_all_algorithms(3). All the symmetric algorithms (ciphers), digests and asymmetric algorithms (public key algorithms) can be replaced by ENGINE modules providing alternative implementations. If ENGINE implementations of ciphers or digests are registered as defaults, then the various EVP functions will automatically use those implementations automatically in preference to built in software implementations. For more information, consult theengine(3)man page. Although low level algorithm specific functions exist for many algorithms their use is discouraged. They cannot be used with an ENGINE and ENGINE versions of new algorithms cannot be accessed using the low level functions. Also makes code harder to adapt to new algorithms and some options are not cleanly supported at the low level and some operations are more efficient using the high level interface.

## SEE ALSO

EVP_DigestInit(3),EVP_EncryptInit(3),EVP_OpenInit(3),EVP_SealInit(3),EVP_DigestSignInit(3),EVP_SignInit(3),EVP_VerifyInit(3),EVP_PKEY_new(3),EVP_PKEY_set1_RSA(3),EVP_PKEY_keygen(3),EVP_PKEY_print_private(3),EVP_PKEY_decrypt(3),EVP_PKEY_encrypt(3),EVP_PKEY_sign(3),EVP_PKEY_verify(3),EVP_PKEY_verify_recover(3),EVP_PKEY_derive(3),EVP_BytesToKey(3),OpenSSL_add_all_algorithms(3),engine(3)1.0.2 2015-01-22 evp(3)

openssl 1.0.2 - Generated Fri Jan 23 11:18:01 CST 2015