EVP_EncryptInit(3)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 rou‐
tines
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 func‐
tion 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 parame‐
ters 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 opera‐
tion 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_Decrypt‐
Final() 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()func‐
tions 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_cipher‐
byobj() 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 correspond‐
ing 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 maxi‐
mum 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 parame‐
ters. 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 exam‐
ple). This function may fail if the cipher does not have any ASN1 sup‐
port.
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. Null
cipher: does nothing. DES in CBC, ECB, CFB and OFB modes respectively.
Two key triple DES in CBC, ECB, CFB and OFB modes respectively. Three
key triple DES in CBC, ECB, CFB and OFB modes respectively. DESX algo‐
rithm in CBC mode. RC4 stream cipher. This is a variable key length
cipher with default key length 128 bits. 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. IDEA encryption algo‐
rithm in CBC, ECB, CFB and OFB modes respectively. RC2 encryption
algorithm in CBC, ECB, CFB and OFB modes respectively. This is a vari‐
able key length cipher with an additional parameter called effective
key bits or effective key length. By default both are set to 128 bits.
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. Blowfish encryption algorithm in CBC, ECB, CFB and OFB modes
respectively. This is a variable key length cipher. CAST encryption
algorithm in CBC, ECB, CFB and OFB modes respectively. This is a vari‐
able key length cipher. 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. Pad‐
ding 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 cor‐
rect 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_CipherUp‐
date(), and EVP_CIPHER_CTX_cleanup() functions did not return errors in
OpenSSL version 0.9.5a or earlier. Software only versions of encryp‐
tion 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 con‐
taining 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 suc‐
cess 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_cipher‐
byobj() 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)EVP_EncryptInit(3)