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BIO_F_CIPHER(3) Library Functions Manual BIO_F_CIPHER(3)

BIO_f_cipher, BIO_set_cipher, BIO_get_cipher_status, BIO_get_cipher_ctxcipher BIO filter

#include <openssl/bio.h>
#include <openssl/evp.h>

const BIO_METHOD *

BIO_set_cipher(BIO *b, const EVP_CIPHER *cipher, unsigned char *key, unsigned char *iv, int enc);

BIO_get_cipher_status(BIO *b);

BIO_get_cipher_ctx(BIO *b, EVP_CIPHER_CTX **pctx);

() returns the cipher BIO method. This is a filter BIO that encrypts any data written through it, and decrypts any data read from it. It is a BIO wrapper for the cipher routines EVP_CipherInit(3), EVP_CipherUpdate(3), and EVP_CipherFinal(3).

Cipher BIOs do not support BIO_gets(3) or BIO_puts(3).

BIO_flush(3) on an encryption BIO that is being written through is used to signal that no more data is to be encrypted: this is used to flush and possibly pad the final block through the BIO.

() sets the cipher of BIO b to cipher using key key and IV iv. enc should be set to 1 for encryption and zero for decryption.

When reading from an encryption BIO, the final block is automatically decrypted and checked when EOF is detected. () is a BIO_ctrl(3) macro which can be called to determine whether the decryption operation was successful.

() is a BIO_ctrl(3) macro which retrieves the internal BIO cipher context. The retrieved context can be used in conjunction with the standard cipher routines to set it up. This is useful when BIO_set_cipher() is not flexible enough for the applications needs.

When encrypting, BIO_flush(3) must be called to flush the final block through the BIO. If it is not, then the final block will fail a subsequent decrypt.

When decrypting, an error on the final block is signalled by a zero return value from the read operation. A successful decrypt followed by EOF will also return zero for the final read. () should be called to determine if the decrypt was successful.

As always, if BIO_gets(3) or BIO_puts(3) support is needed, then it can be achieved by preceding the cipher BIO with a buffering BIO.

BIO_f_cipher() returns the cipher BIO method. BIO_set_cipher() returns 1 on success and 0 on error.

BIO_get_cipher_status() returns 1 for a successful decrypt and 0 for failure.

BIO_get_cipher_ctx() currently always returns 1.

BIO_new(3), EVP_EncryptInit(3)

BIO_f_cipher(), BIO_set_cipher(), and BIO_get_cipher_status() first appeared in SSLeay 0.6.5 and have been available since OpenBSD 2.4.

BIO_get_cipher_ctx() first appeared in SSLeay 0.9.1 and has been available since OpenBSD 2.6.

June 6, 2019 OpenBSD-current