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EVP_EncryptInit(3)
NAME
EVP_EncryptInit, EVP_EncryptUpdate, EVP_EncryptFinal, EVP_DecryptInit,
EVP_DecryptUpdate, EVP_DecryptFinal, EVP_CipherInit, EVP_CipherUpdate,
EVP_CipherFinal, EVP_CIPHER_CTX_set_key_length, EVP_CIPHER_CTX_ctrl,
EVP_CIPHER_CTX_cleanup, EVP_get_cipherbyname, EVP_get_cipherbynid,
EVP_get_cipherbyobj, EVP_CIPHER_nid, EVP_CIPHER_block_size,
EVP_CIPHER_key_length, EVP_CIPHER_iv_length, EVP_CIPHER_flags,
EVP_CIPHER_mode, EVP_CIPHER_type, EVP_CIPHER_CTX_cipher,
EVP_CIPHER_CTX_nid, EVP_CIPHER_CTX_block_size, EVP_CIPHER_CTX_key_length,
EVP_CIPHER_CTX_iv_length, EVP_CIPHER_CTX_get_app_data,
EVP_CIPHER_CTX_set_app_data, EVP_CIPHER_CTX_type, EVP_CIPHER_CTX_flags,
EVP_CIPHER_CTX_mode, EVP_CIPHER_param_to_asn1, EVP_CIPHER_asn1_to_param -
EVP cipher routines
SYNOPSIS
#include <openssl/evp.h>
int EVP_EncryptInit(
EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, unsigned
char *key, unsigned char *iv );
int EVP_EncryptUpdate(
EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl,
unsigned char *in, int inl );
int EVP_EncryptFinal(
EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl );
int EVP_DecryptInit(
EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, unsigned
char *key, unsigned char *iv );
int EVP_DecryptUpdate(
EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl,
unsigned char *in, int inl );
int EVP_DecryptFinal(
EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl );
int EVP_CipherInit(
EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, unsigned
char *key, unsigned char *iv, int enc );
int EVP_CipherUpdate(
EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl,
unsigned char *in, int inl );
int EVP_CipherFinal(
EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl );
int EVP_CIPHER_CTX_set_key_length(
EVP_CIPHER_CTX *x, int keylen );
int EVP_CIPHER_CTX_ctrl(
EVP_CIPHER_CTX *ctx, int type, int arg, void *ptr );
int EVP_CIPHER_CTX_cleanup(
EVP_CIPHER_CTX *a );
const EVP_CIPHER *EVP_get_cipherbyname(
const char *name );
#define EVP_get_cipherbynid(a) EVP_get_cipherbyname(OBJ_nid2sn(a))
#define EVP_get_cipherbyobj(a) EVP_get_cipherbynid(OBJ_obj2nid(a))
#define EVP_CIPHER_nid(e) ((e)->nid)
#define EVP_CIPHER_block_size(e) ((e)->block_size)
#define EVP_CIPHER_key_length(e) ((e)->key_len)
#define EVP_CIPHER_iv_length(e) ((e)->iv_len)
#define EVP_CIPHER_flags(e) ((e)->flags)
#define EVP_CIPHER_mode(e) ((e)->flags) & EVP_CIPH_MODE)
int EVP_CIPHER_type(
const EVP_CIPHER *ctx );
#define EVP_CIPHER_CTX_cipher(e) ((e)->cipher)
#define EVP_CIPHER_CTX_nid(e) ((e)->cipher->nid)
#define EVP_CIPHER_CTX_block_size(e) ((e)->cipher->block_size)
#define EVP_CIPHER_CTX_key_length(e) ((e)->key_len)
#define EVP_CIPHER_CTX_iv_length(e) ((e)->cipher->iv_len)
#define EVP_CIPHER_CTX_get_app_data(e) ((e)->app_data)
#define EVP_CIPHER_CTX_set_app_data(e,d) ((e)->app_data=(char *)(d))
#define EVP_CIPHER_CTX_type(c) EVP_CIPHER_type(EVP_CIPHER_CTX_cipher(c))
#define EVP_CIPHER_CTX_flags(e) ((e)->cipher->flags)
#define EVP_CIPHER_CTX_mode(e) ((e)->cipher->flags &
EVP_CIPH_MODE)
int EVP_CIPHER_param_to_asn1(
EVP_CIPHER_CTX *c, ASN1_TYPE *type );
int EVP_CIPHER_asn1_to_param(
EVP_CIPHER_CTX *c, ASN1_TYPE *type );
DESCRIPTION
The EVP cipher routines are a high level interface to certain symmetric
ciphers.
The EVP_EncryptInit() function initializes a cipher context ctx for
encryption with cipher type. The type is usually supplied by a function
such as EVP_des_cbc().The 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. 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.
The EVP_EncryptUpdate() function encrypts inl 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 (inl +
cipher_block_size - 1); so outl should contain sufficient room. The actual
number of bytes written is placed in outl.
The EVP_EncryptFinal() function encrypts the final data, that is any data
that remains in a partial block. It uses standard block padding (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 outl. After this function is called the encryption operation is
finished and no further calls to EVP_EncryptUpdate() should be made.
The EVP_DecryptInit(), EVP_DecryptUpdate(), and EVP_DecryptFinal()
functions are the corresponding decryption operations. The
EVP_DecryptFinal() function will return an error code if the final block is
not formatted correctly. The parameters and restrictions are identical to
the encryption operations except that the decrypted data buffer out passed
to EVP_DecryptUpdate() should have sufficient room for (inl +
cipher_block_size) bytes unless the cipher block size is 1 in which case
inl bytes is sufficient.
The EVP_CipherInit(), EVP_CipherUpdate(), and EVP_CipherFinal()functions
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).
The EVP_CIPHER_CTX_cleanup() function clears all information from a cipher
context. It should be called after all operations using a cipher are
complete so sensitive information does not remain in memory.
The EVP_get_cipherbyname(), EVP_get_cipherbynid(), and
EVP_get_cipherbyobj() functions return an EVP_CIPHER structure when passed
a cipher name, a NID or an ASN1_OBJECT structure.
The EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() functions return the NID of a
cipher when passed an EVP_CIPHER or EVP_CIPHER_CTX structure. The actual
NID value is an internal value which may not have a corresponding OBJECT
IDENTIFIER.
The EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() function return
the key length of a cipher when passed an EVP_CIPHER or EVP_CIPHER_CTX
structure. The constant EVP_MAX_KEY_LENGTH is the maximum key length for
all ciphers. Although the EVP_CIPHER_key_length() function is fixed for a
given cipher, the value of the EVP_CIPHER_CTX_key_length() function may be
different for variable key length ciphers.
The EVP_CIPHER_CTX_set_key_length() function sets the key length of the
cipher ctx. If the cipher is a fixed length cipher then attempting to set
the key length to any value other than the fixed value is an error.
The EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() functions return
the IV length of a cipher when passed an EVP_CIPHER or EVP_CIPHER_CTX. It
will return zero if the cipher does not use an IV. The constant
EVP_MAX_IV_LENGTH is the maximum IV length for all ciphers.
The EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() functions
return the block size of a cipher when passed an EVP_CIPHER or
EVP_CIPHER_CTX structure. The constant EVP_MAX_IV_LENGTH is also the
maximum block length for all ciphers.
The EVP_CIPHER_type() and EVP_CIPHER_CTX_type() functions return the type
of the passed cipher or context. This type is the actual NID of the cipher
OBJECT IDENTIFIER. As such, it ignores the cipher parameters. and 40 bit
RC2 and 128 bit RC2 have the same NID. If the cipher does not have an
object identifier or does not have ASN1 support this function will return
NID_undef.
The EVP_CIPHER_CTX_cipher() function returns the EVP_CIPHER structure when
passed an EVP_CIPHER_CTX structure.
The EVP_CIPHER_mode() and EVP_CIPHER_CTX_mode() functions return the block
cipher mode: EVP_CIPH_ECB_MODE, EVP_CIPH_CBC_MODE, EVP_CIPH_CFB_MODE, or
EVP_CIPH_OFB_MODE. If the cipher is a stream cipher then
EVP_CIPH_STREAM_CIPHER is returned.
The EVP_CIPHER_param_to_asn1() function sets the AlgorithmIdentifier
parameter based on the passed cipher. This typically will include any
parameters and an IV. The cipher IV (if any) must be set when this call is
made. This call should be made before the cipher is actually used (before
any EVP_EncryptUpdate() or EVP_DecryptUpdate() calls, for example). This
function may fail if the cipher does not have any ASN1 support.
The EVP_CIPHER_asn1_to_param() function sets the cipher parameters based on
an ASN1 AlgorithmIdentifier parameter. The precise effect depends on the
cipher In the case of RC2, for example, it will set the IV and effective
key length. This function should be called after the base cipher type is
set but before the key is set. For example, the EVP_CipherInit() function
will be called with the IV and key set to NULL. The
EVP_CIPHER_asn1_to_param() function will be called and finally the
EVP_CipherInit() function. All parameters except the key are set to NULL.
It is possible for this function to fail if the cipher does not have any
ASN1 support or the parameters cannot be set (for example the RC2 effective
key length is not supported).
The EVP_CIPHER_CTX_ctrl() function allows various cipher specific
parameters to be determined and set. Currently only the RC2 effective key
length and the number of rounds of RC5 can be set.
Cipher Listing
All algorithms have a fixed key length unless otherwise stated.
EVP_enc_null()
Null cipher: does nothing.
EVP_des_cbc(void), EVP_des_ecb(void), EVP_des_cfb(void), EVP_des_ofb(void)
DES in CBC, ECB, CFB and OFB modes respectively.
EVP_des_ede_cfb(void)
EVP_des_ede_cbc(void), EVP_des_ede(), EVP_des_ede_ofb(void),
Two key triple DES in CBC, ECB, CFB and OFB modes respectively.
EVP_des_ede3_cfb(void)
EVP_des_ede3_cbc(void), EVP_des_ede3(), EVP_des_ede3_ofb(void),
Three key triple DES in CBC, ECB, CFB and OFB modes respectively.
EVP_desx_cbc(void)
DESX algorithm in CBC mode.
EVP_rc4(void)
RC4 stream cipher. This is a variable key length cipher with
default key length 128 bits.
EVP_rc4_40(void)
RC4 stream cipher with 40 bit key length. This is obsolete and new
code should use the EVP_rc4()and the
EVP_CIPHER_CTX_set_key_length() functions.
EVP_idea_cbc(void)
EVP_idea_cbc() EVP_idea_ecb(void), EVP_idea_cfb(void), EVP_idea_ofb(void),
IDEA encryption algorithm in CBC, ECB, CFB and OFB modes
respectively.
EVP_rc2_cbc(void), EVP_rc2_ecb(void), EVP_rc2_cfb(void), EVP_rc2_ofb(void)
RC2 encryption algorithm in CBC, ECB, CFB and OFB modes
respectively. This is a variable key length cipher with an
additional parameter called effective key bits or effective key
length. By default both are set to 128 bits.
EVP_rc2_40_cbc(void), EVP_rc2_64_cbc(void)
RC2 algorithm in CBC mode with a default key length and effective
key length of 40 and 64 bits. These are obsolete and new code
should use the EVP_rc2_cbc(), EVP_CIPHER_CTX_set_key_length(), and
EVP_CIPHER_CTX_ctrl() functions to set the key length and effective
key length.
EVP_bf_cbc(void), EVP_bf_ecb(void), EVP_bf_cfb(void), EVP_bf_ofb(void);
Blowfish encryption algorithm in CBC, ECB, CFB and OFB modes
respectively. This is a variable key length cipher.
EVP_cast5_ofb(void)
EVP_cast5_cbc(void), EVP_cast5_ecb(void), EVP_cast5_cfb(void),
CAST encryption algorithm in CBC, ECB, CFB and OFB modes
respectively. This is a variable key length cipher.
EVP_rc5_32_12_16_cfb(void), EVP_rc5_32_12_16_ofb(void)
EVP_rc5_32_12_16_cbc(void), EVP_rc5_32_12_16_ecb(void),
RC5 encryption algorithm in CBC, ECB, CFB and OFB modes
respectively. This is a variable key length cipher with an
additional "number of rounds parameter. By default the key length
is set to 128 bits and 12 rounds.
NOTES
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, it is not a strong
test that the input data or key is correct. A random block has better than
a 1-in- 256 chance of being of the correct format. Problems with the input
data earlier on will not produce a final decrypt error.
The EVP_EncryptInit(), EVP_EncryptUpdate(), EVP_EncryptFinal(),
EVP_DecryptInit(), EVP_DecryptUpdate(), EVP_CipherInit(),
EVP_CipherUpdate(), and EVP_CIPHER_CTX_cleanup() functions did not return
errors in OpenSSL version 0.9.5a or earlier. Software only versions of
encryption algorithms will never return error codes for these functions,
unless there is a programming error (for example, an attempt to set the key
before the cipher is set in EVP_EncryptInit()).
RESTRICTIONS
For RC5 the number of rounds can be set only to 8, 12 or 16. This is a
limitation of the current RC5 code rather than the EVP interface.
It is not possible to disable PKCS padding.
EVP_MAX_KEY_LENGTH and EVP_MAX_IV_LENGTH only refer to the internal ciphers
with default key lengths. If custom ciphers exceed these values the results
are unpredictable. This is because it has become standard practice to
define a generic key as a fixed unsigned char array containing
EVP_MAX_KEY_LENGTH bytes.
The ASN1 code is incomplete (and sometimes inaccurate). It has only been
tested for certain common S/MIME ciphers (RC2, DES, triple DES) in CBC
mode.
RETURN VALUES
The EVP_EncryptInit(), EVP_EncryptUpdate(), and EVP_EncryptFinal()
functions return 1 for success and 0 for failure.
The EVP_DecryptInit() and EVP_DecryptUpdate() functions return 1 for
success and 0 for failure. The EVP_DecryptFinal() function returns 0 if the
decrypt failed or 1 for success.
The EVP_CipherInit() and EVP_CipherUpdate() functions return 1 for success
and 0 for failure.
The EVP_CipherFinal() function returns 0 for a decryption failure or 1 for
success.
The EVP_CIPHER_CTX_cleanup() function returns 1 for success and 0 for
failure.
The EVP_get_cipherbyname(), EVP_get_cipherbynid(), and
EVP_get_cipherbyobj() functions return an EVP_CIPHER structure or NULL on
error.
The EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() functions return a NID.
The EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() functions
return the block size.
The EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() functions
return the key length.
The EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() functions return
the IV length or zero if the cipher does not use an IV.
The EVP_CIPHER_type() and EVP_CIPHER_CTX_type() functions return the NID of
the cipher's OBJECT IDENTIFIER or NID_undef if it has no defined OBJECT
IDENTIFIER.
The EVP_CIPHER_CTX_cipher() function returns an EVP_CIPHER structure.
The EVP_CIPHER_param_to_asn1() and EVP_CIPHER_asn1_to_param() functions
return 1 for success or zero for failure.
EXAMPLES
Get the number of rounds used in RC5:
int nrounds;
EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GET_RC5_ROUNDS, 0, &i);
Get the RC2 effective key length:
int key_bits;
EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GET_RC2_KEY_BITS, 0, &i);
Set the number of rounds used in RC5:
int nrounds;
EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_SET_RC5_ROUNDS, i, NULL);
Set the number of rounds used in RC2:
int nrounds;
EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_SET_RC2_KEY_BITS, i, NULL);
SEE ALSO
Functions: evp(3)
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