NAME
EVP_CIPHER_CTX_new,
EVP_CIPHER_CTX_reset,
EVP_CIPHER_CTX_free,
EVP_CIPHER_CTX_copy,
EVP_EncryptInit_ex,
EVP_EncryptUpdate,
EVP_EncryptFinal_ex,
EVP_DecryptInit_ex,
EVP_DecryptUpdate,
EVP_DecryptFinal_ex,
EVP_CipherInit_ex,
EVP_CipherUpdate,
EVP_CipherFinal_ex,
EVP_EncryptInit,
EVP_EncryptFinal,
EVP_DecryptInit,
EVP_DecryptFinal,
EVP_CipherInit,
EVP_CipherFinal,
EVP_CIPHER_CTX_encrypting,
EVP_get_cipherbyname,
EVP_get_cipherbynid,
EVP_get_cipherbyobj,
EVP_CIPHER_CTX_cipher,
EVP_enc_null, EVP_idea_cbc,
EVP_idea_ecb,
EVP_idea_cfb64,
EVP_idea_cfb, EVP_idea_ofb,
EVP_bf_cbc, EVP_bf_ecb,
EVP_bf_cfb64, EVP_bf_cfb,
EVP_bf_ofb, EVP_cast5_cbc,
EVP_cast5_ecb,
EVP_cast5_cfb64,
EVP_cast5_cfb, EVP_cast5_ofb
— EVP cipher routines
SYNOPSIS
#include
<openssl/evp.h>
EVP_CIPHER_CTX *
EVP_CIPHER_CTX_new(void);
int
EVP_CIPHER_CTX_reset(EVP_CIPHER_CTX
*ctx);
void
EVP_CIPHER_CTX_free(EVP_CIPHER_CTX
*ctx);
int
EVP_CIPHER_CTX_copy(EVP_CIPHER_CTX
*out, const EVP_CIPHER_CTX *in);
int
EVP_EncryptInit_ex(EVP_CIPHER_CTX
*ctx, const EVP_CIPHER *type,
ENGINE *engine, const unsigned char
*key, const unsigned char *iv);
int
EVP_EncryptUpdate(EVP_CIPHER_CTX
*ctx, unsigned char *out, int
*out_len, const unsigned char *in,
int in_len);
int
EVP_EncryptFinal_ex(EVP_CIPHER_CTX
*ctx, unsigned char *out, int
*out_len);
int
EVP_DecryptInit_ex(EVP_CIPHER_CTX
*ctx, const EVP_CIPHER *type,
ENGINE *engine, const unsigned char
*key, const unsigned char *iv);
int
EVP_DecryptUpdate(EVP_CIPHER_CTX
*ctx, unsigned char *out, int
*out_len, const unsigned char *in,
int in_len);
int
EVP_DecryptFinal_ex(EVP_CIPHER_CTX
*ctx, unsigned char *out, int
*out_len);
int
EVP_CipherInit_ex(EVP_CIPHER_CTX
*ctx, const EVP_CIPHER *type,
ENGINE *engine, const unsigned char
*key, const unsigned char *iv,
int enc);
int
EVP_CipherUpdate(EVP_CIPHER_CTX
*ctx, unsigned char *out, int
*out_len, const unsigned char *in,
int in_len);
int
EVP_CipherFinal_ex(EVP_CIPHER_CTX
*ctx, unsigned char *out, int
*out_len);
int
EVP_EncryptInit(EVP_CIPHER_CTX
*ctx, const EVP_CIPHER *type,
const unsigned char *key, const
unsigned char *iv);
int
EVP_EncryptFinal(EVP_CIPHER_CTX
*ctx, unsigned char *out, int
*out_len);
int
EVP_DecryptInit(EVP_CIPHER_CTX
*ctx, const EVP_CIPHER *type,
const unsigned char *key, const
unsigned char *iv);
int
EVP_DecryptFinal(EVP_CIPHER_CTX
*ctx, unsigned char *out, int
*out_len);
int
EVP_CipherInit(EVP_CIPHER_CTX
*ctx, const EVP_CIPHER *type,
const unsigned char *key, const
unsigned char *iv, int enc);
int
EVP_CipherFinal(EVP_CIPHER_CTX
*ctx, unsigned char *out, int
*out_len);
int
EVP_CIPHER_CTX_encrypting(const
EVP_CIPHER_CTX *ctx);
const EVP_CIPHER *
EVP_get_cipherbyname(const char
*name);
const EVP_CIPHER *
EVP_get_cipherbynid(int
nid);
const EVP_CIPHER *
EVP_get_cipherbyobj(const ASN1_OBJECT
*a);
const EVP_CIPHER *
EVP_CIPHER_CTX_cipher(const
EVP_CIPHER_CTX *ctx);
DESCRIPTION
The EVP cipher routines are a high level interface to certain symmetric ciphers.
EVP_CIPHER_CTX_new()
creates a new, empty cipher context.
EVP_CIPHER_CTX_reset()
clears all information from ctx and frees all
allocated memory associated with it, except the ctx
object itself, such that it can be reused for another series of calls to
EVP_CipherInit(),
EVP_CipherUpdate(),
and
EVP_CipherFinal().
EVP_CIPHER_CTX_free()
clears all information from ctx and frees all
allocated memory associated with it, including ctx
itself. This function should be called after all operations using a cipher
are complete, so sensitive information does not remain in memory. If
ctx is a NULL pointer, no
action occurs.
EVP_CIPHER_CTX_copy()
calls EVP_CIPHER_CTX_reset() on
out and copies all the data from
in to out, except that the
EVP_CIPHER object used by in and
any application specific data set with
EVP_CIPHER_CTX_set_app_data(3) are not copied and
out will point to the same two objects. The algorithm-
and implementation-specific cipher data described in
EVP_CIPHER_CTX_get_cipher_data(3) is copied with
malloc(3)
and memcpy(3), i.e. assuming that it does not contain pointers to any
sub-objects. If the bit EVP_CIPH_CUSTOM_COPY has
been set with
EVP_CIPHER_meth_set_flags(3),
EVP_CIPHER_CTX_ctrl(3) is called at the end with arguments
in, EVP_CTRL_COPY,
0, and out such that the
cipher implementation can perform further algorithm- and
implementation-specific initializations after the algorithm- and
implementation-specific cipher data has been copied. Among the cipher
algorithms built into the library,
EVP_CIPH_CUSTOM_COPY and
EVP_CTRL_COPY are used by some of the ciphers
documented in the
EVP_aes_256_gcm(3) manual page.
EVP_EncryptInit()
and
EVP_EncryptInit_ex()
set up the cipher context ctx for encryption with
cipher type. type is normally
supplied by a function such as
EVP_aes_256_cbc(3). key is the symmetric key to
use and iv is the IV to use (if necessary). The actual
number of bytes used for the key and IV depends on the cipher. The
ENGINE *engine argument is always ignored and passing
NULL is recommended. It is possible to set all
parameters to NULL except type
in an initial call and supply the remaining parameters in subsequent calls,
all of which have type set to
NULL. This is done when the default cipher
parameters are not appropriate.
EVP_EncryptUpdate()
encrypts in_len bytes from the buffer
in and writes the encrypted version to
out. This function can be called multiple times to
encrypt successive blocks of data. The amount of data written depends on the
block alignment of the encrypted data: as a result the amount of data
written may be anything from zero bytes to (in_len
+ cipher_block_size - 1) so
out should contain sufficient room. The actual number
of bytes written is placed in *out_len.
If padding is enabled (the default) then
EVP_EncryptFinal()
and
EVP_EncryptFinal_ex(),
which behave identically, encrypt the "final" data, that is any
data that remains in a partial block. It uses NOTES (aka PKCS padding). The
encrypted final data is written to out which should
have sufficient space for one cipher block. The number of bytes written is
placed in *out_len. After this function is called, the
encryption operation is finished and no further calls to
EVP_EncryptUpdate() should be made.
If padding is disabled then
EVP_EncryptFinal()
and
EVP_EncryptFinal_ex()
do not encrypt any more data and return an error if any data remains in a
partial block: that is if the total data length is not a multiple of the
block size.
EVP_DecryptInit(),
EVP_DecryptInit_ex(),
EVP_DecryptUpdate(),
EVP_DecryptFinal(),
and
EVP_DecryptFinal_ex()
are the corresponding decryption operations.
EVP_DecryptFinal() and
EVP_DecryptFinal_ex() return an error code if
padding is enabled and the final block is not correctly formatted. The
parameters and restrictions are identical to the encryption operations
except that if padding is enabled the decrypted data buffer
out passed to
EVP_DecryptUpdate() should have sufficient room for
(in_len + cipher_block_size)
bytes unless the cipher block size is 1 in which case
in_len bytes is sufficient.
EVP_CipherInit(),
EVP_CipherInit_ex(),
EVP_CipherUpdate(),
EVP_CipherFinal(),
and
EVP_CipherFinal_ex()
are functions that can be used for decryption or encryption. The operation
performed depends on the value of the enc parameter.
It should be set to 1 for encryption, 0 for decryption and -1 to leave the
value unchanged (the actual value of enc being
supplied in a previous call).
EVP_get_cipherbyname(),
EVP_get_cipherbynid(), and
EVP_get_cipherbyobj() return an
EVP_CIPHER structure when passed a cipher name, a NID
or an ASN1_OBJECT structure.
EVP_CIPHER_CTX_cipher()
returns the EVP_CIPHER structure when passed an
EVP_CIPHER_CTX structure.
Where possible the EVP interface to symmetric ciphers should be used in preference to the low level interfaces. This is because the code then becomes transparent to the cipher used and much more flexible.
PKCS padding works by adding n padding bytes of value n to make the total length of the encrypted data a multiple of the block size. Padding is always added so if the data is already a multiple of the block size n will equal the block size. For example if the block size is 8 and 11 bytes are to be encrypted then 5 padding bytes of value 5 will be added.
When decrypting, the final block is checked to see if it has the correct form.
Although the decryption operation can produce an error if padding is enabled, it is not a strong test that the input data or key is correct. A random block has better than 1 in 256 chance of being of the correct format and problems with the input data earlier on will not produce a final decrypt error.
If padding is disabled then the decryption operation will always succeed if the total amount of data decrypted is a multiple of the block size.
EVP_get_cipherbynid()
and
EVP_get_cipherbyobj()
are implemented as macros.
RETURN VALUES
EVP_CIPHER_CTX_new() returns a pointer to
a newly created EVP_CIPHER_CTX for success or
NULL for failure.
EVP_CIPHER_CTX_reset(),
EVP_CIPHER_CTX_copy(),
EVP_EncryptInit_ex(),
EVP_EncryptUpdate(),
EVP_EncryptFinal_ex(),
EVP_DecryptInit_ex(),
EVP_DecryptUpdate(),
EVP_DecryptFinal_ex(),
EVP_CipherInit_ex(),
EVP_CipherUpdate(),
EVP_CipherFinal_ex(),
EVP_EncryptInit(),
EVP_EncryptFinal(),
EVP_DecryptInit(),
EVP_DecryptFinal(),
EVP_CipherInit(), and
EVP_CipherFinal() return 1 for success or 0 for
failure.
EVP_CIPHER_CTX_encrypting() returns 1 if
ctx is initialized for encryption or 0 otherwise, in
which case it may be uninitialized or initialized for decryption.
EVP_get_cipherbyname(),
EVP_get_cipherbynid(), and
EVP_get_cipherbyobj() return an
EVP_CIPHER structure or NULL
on error.
EVP_CIPHER_CTX_cipher() returns an
EVP_CIPHER structure.
CIPHER LISTING
EVP_enc_null()- Null cipher: does nothing.
EVP_idea_cbc(),EVP_idea_ecb(),EVP_idea_cfb64(),EVP_idea_ofb()- IDEA encryption algorithm in CBC, ECB, CFB and OFB modes respectively.
IDEA is a block cipher operating on 64 bit blocks using a 128 bit
key.
EVP_idea_cfb() is an alias forEVP_idea_cfb64(), implemented as a macro. EVP_bf_cbc(),EVP_bf_ecb(),EVP_bf_cfb64(),EVP_bf_ofb()- Blowfish encryption algorithm in CBC, ECB, CFB and OFB modes respectively.
Blowfish is a block cipher operating on 64 bit blocks using a variable
key length. The default key length is 128 bits.
EVP_bf_cfb() is an alias forEVP_bf_cfb64(), implemented as a macro. EVP_cast5_cbc(),EVP_cast5_ecb(),EVP_cast5_cfb64(),EVP_cast5_ofb()- CAST-128 encryption algorithm in CBC, ECB, CFB and OFB modes respectively.
CAST-128 is a block cipher operating on 64 bit blocks using a variable
key length. The default and maximum key length is
128 bits.
EVP_cast5_cfb() is an alias forEVP_cast5_cfb64(), implemented as a macro.
Some algorithms are documented in separate manual pages:
| manual page | block size | key size (in bits) |
| EVP_aes_128_cbc(3) | 128 | 128, 192, 256 |
| EVP_aes_128_ccm(3) | 128 | 128, 192, 256 |
| EVP_aes_128_gcm(3) | 128 | 128, 192, 256 |
| EVP_camellia_128_cbc(3) | 128 | 128, 192, 256 |
| EVP_chacha20(3) | stream | 256 |
| EVP_des_cbc(3) | 64 | 64 |
| EVP_rc2_cbc(3) | 64 | variable, default 128 |
| EVP_rc4(3) | stream | variable, default 128 |
| EVP_sm4_cbc(3) | 128 | 128 |
EXAMPLES
Encrypt a string using blowfish:
int
do_crypt(char *out_filename)
{
unsigned char out_buf[1024];
int out_len, tmp_len;
/*
* Bogus key and IV: we'd normally set these from
* another source.
*/
unsigned char key[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
unsigned char iv[] = {1,2,3,4,5,6,7,8};
const char in_text[] = "Some Crypto Text";
EVP_CIPHER_CTX *ctx;
FILE *out_fileptr;
ctx = EVP_CIPHER_CTX_new();
EVP_EncryptInit_ex(ctx, EVP_bf_cbc(), NULL, key, iv);
if (!EVP_EncryptUpdate(ctx, out_buf, &out_len, in_text,
strlen(in_text))) {
/* Error */
EVP_CIPHER_CTX_free(ctx);
return 0;
}
/*
* Buffer passed to EVP_EncryptFinal() must be after data just
* encrypted to avoid overwriting it.
*/
if (!EVP_EncryptFinal_ex(ctx, out_buf + out_len, &tmp_len)) {
/* Error */
EVP_CIPHER_CTX_free(ctx);
return 0;
}
out_len += tmp_len;
EVP_CIPHER_CTX_free(ctx);
/*
* Need binary mode for fopen because encrypted data is
* binary data. Also cannot use strlen() on it because
* it won't be NUL terminated and may contain embedded
* NULs.
*/
out_fileptr = fopen(out_filename, "wb");
if (out_fileptr == NULL) {
/* Error */
return 0;
}
fwrite(out_buf, 1, out_len, out_fileptr);
fclose(out_fileptr);
return 1;
}
The ciphertext from the above example can be decrypted using the openssl(1) utility with the command line:
openssl bf -in cipher.bin -K 000102030405060708090A0B0C0D0E0F \
-iv 0102030405060708 -d
General encryption, decryption function example using FILE I/O and AES128 with a 128-bit key:
int
do_crypt(FILE *in_fileptr, FILE *out_fileptr, int do_encrypt)
{
/* Allow enough space in output buffer for additional block */
unsigned char in_buf[1024], out_buf[1024 + EVP_MAX_BLOCK_LENGTH];
int in_len, out_len;
EVP_CIPHER_CTX *ctx;
/*
* Bogus key and IV: we'd normally set these from
* another source.
*/
unsigned char key[] = "0123456789abcdeF";
unsigned char iv[] = "1234567887654321";
ctx = EVP_CIPHER_CTX_new();
EVP_CipherInit_ex(ctx, EVP_aes_128_cbc(), NULL, NULL, NULL,
do_encrypt);
EVP_CipherInit_ex(ctx, NULL, NULL, key, iv, do_encrypt);
for (;;) {
in_len = fread(in_buf, 1, 1024, in_fileptr);
if (in_len <= 0)
break;
if (!EVP_CipherUpdate(ctx, out_buf, &out_len, in_buf,
in_len)) {
/* Error */
EVP_CIPHER_CTX_free(ctx);
return 0;
}
fwrite(out_buf, 1, out_len, out_fileptr);
}
if (!EVP_CipherFinal_ex(ctx, out_buf, &out_len)) {
/* Error */
EVP_CIPHER_CTX_free(ctx);
return 0;
}
fwrite(out_buf, 1, out_len, out_fileptr);
EVP_CIPHER_CTX_free(ctx);
return 1;
}
SEE ALSO
BIO_f_cipher(3), evp(3), EVP_AEAD_CTX_init(3), EVP_aes_128_cbc(3), EVP_aes_128_ccm(3), EVP_aes_128_gcm(3), EVP_camellia_128_cbc(3), EVP_chacha20(3), EVP_CIPHER_CTX_ctrl(3), EVP_CIPHER_CTX_get_cipher_data(3), EVP_CIPHER_CTX_init(3), EVP_CIPHER_CTX_set_flags(3), EVP_CIPHER_nid(3), EVP_des_cbc(3), EVP_OpenInit(3), EVP_rc2_cbc(3), EVP_rc4(3), EVP_SealInit(3), EVP_sm4_cbc(3)
HISTORY
EVP_EncryptInit(),
EVP_EncryptUpdate(),
EVP_EncryptFinal(),
EVP_DecryptInit(),
EVP_DecryptUpdate(),
EVP_DecryptFinal(),
EVP_CipherInit(),
EVP_CipherUpdate(),
EVP_CipherFinal(),
EVP_get_cipherbyname(),
EVP_idea_cbc(),
EVP_idea_ecb(),
EVP_idea_cfb(), and
EVP_idea_ofb() first appeared in SSLeay 0.5.1.
EVP_bf_cbc(), EVP_bf_ecb(),
EVP_bf_cfb(), and
EVP_bf_ofb() first appeared in SSLeay 0.6.6.
EVP_get_cipherbyobj(),
EVP_CIPHER_CTX_cipher(), and
EVP_enc_null() first appeared in SSLeay 0.8.0.
EVP_get_cipherbynid() first appeared in SSLeay
0.8.1. All these functions have been available since
OpenBSD 2.4.
EVP_EncryptInit_ex(),
EVP_EncryptFinal_ex(),
EVP_DecryptInit_ex(),
EVP_DecryptFinal_ex(),
EVP_CipherInit_ex(), and
EVP_CipherFinal_ex() first appeared in OpenSSL 0.9.7
and have been available since OpenBSD 3.2.
EVP_bf_cfb64(),
EVP_cast5_cfb64(), and
EVP_idea_cfb64() first appeared in OpenSSL 0.9.7e
and have been available since OpenBSD 3.8.
EVP_CIPHER_CTX_new() and
EVP_CIPHER_CTX_free() first appeared in OpenSSL
0.9.8b and have been available since OpenBSD
4.5.
EVP_CIPHER_CTX_copy() first appeared in
OpenSSL 1.0.0 and has been available since OpenBSD
4.9.
EVP_CIPHER_CTX_reset() first appeared in
OpenSSL 1.1.0 and has been available since OpenBSD
6.3.
EVP_CIPHER_CTX_encrypting() first appeared
in OpenSSL 1.1.0 and has been available since OpenBSD
6.4.
BUGS
EVP_CIPHER_CTX_copy() may already have
cleared the data in out and copied some new data into
it even if it fails and returns 0.