EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
NAME
EVP_CIPHER_CTX_init, 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_CIPHER_CTX_set_key_length, EVP_CIPHER_CTX_ctrl,
EVP_CIPHER_CTX_cleanup, EVP_EncryptInit, EVP_EncryptFinal,
EVP_DecryptInit, EVP_DecryptFinal, EVP_CipherInit, EVP_CipherFinal,
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_CTX_set_padding, EVP_enc_null,
EVP_des_cbc, EVP_des_ecb, EVP_des_cfb, EVP_des_ofb, EVP_des_ede_cbc,
EVP_des_ede, EVP_des_ede_ofb, EVP_des_ede_cfb, EVP_des_ede3_cbc,
EVP_des_ede3, EVP_des_ede3_ofb, EVP_des_ede3_cfb, EVP_desx_cbc,
EVP_rc4, EVP_rc4_40, EVP_idea_cbc, EVP_idea_ecb, EVP_idea_cfb,
EVP_idea_ofb, EVP_idea_cbc, EVP_rc2_cbc, EVP_rc2_ecb, EVP_rc2_cfb,
EVP_rc2_ofb, EVP_rc2_40_cbc, EVP_rc2_64_cbc, EVP_bf_cbc, EVP_bf_ecb,
EVP_bf_cfb, EVP_bf_ofb, EVP_cast5_cbc, EVP_cast5_ecb, EVP_cast5_cfb,
EVP_cast5_ofb, EVP_rc5_32_12_16_cbc, EVP_rc5_32_12_16_ecb,
EVP_rc5_32_12_16_cfb, EVP_rc5_32_12_16_ofb, EVP_aes_128_gcm,
EVP_aes_192_gcm, EVP_aes_256_gcm, EVP_aes_128_ccm, EVP_aes_192_ccm,
EVP_aes_256_ccm - EVP cipher routines
SYNOPSIS
#include <openssl/evp.h>
void EVP_CIPHER_CTX_init(EVP_CIPHER_CTX *a);
int EVP_EncryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
ENGINE *impl, 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_ex(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl);
int EVP_DecryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
ENGINE *impl, 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_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm,
int *outl);
int EVP_CipherInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
ENGINE *impl, 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_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm,
int *outl);
int EVP_EncryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
unsigned char *key, unsigned char *iv);
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_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_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm,
int *outl);
int EVP_CIPHER_CTX_set_padding(EVP_CIPHER_CTX *x, int padding);
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);
const EVP_CIPHER *EVP_des_ede3(void);
const EVP_CIPHER *EVP_des_ede3_ecb(void);
const EVP_CIPHER *EVP_des_ede3_cfb64(void);
const EVP_CIPHER *EVP_des_ede3_cfb1(void);
const EVP_CIPHER *EVP_des_ede3_cfb8(void);
const EVP_CIPHER *EVP_des_ede3_ofb(void);
const EVP_CIPHER *EVP_des_ede3_cbc(void);
const EVP_CIPHER *EVP_aes_128_ecb(void);
const EVP_CIPHER *EVP_aes_128_cbc(void);
const EVP_CIPHER *EVP_aes_128_cfb1(void);
const EVP_CIPHER *EVP_aes_128_cfb8(void);
const EVP_CIPHER *EVP_aes_128_cfb128(void);
const EVP_CIPHER *EVP_aes_128_ofb(void);
const EVP_CIPHER *EVP_aes_192_ecb(void);
const EVP_CIPHER *EVP_aes_192_cbc(void);
const EVP_CIPHER *EVP_aes_192_cfb1(void);
const EVP_CIPHER *EVP_aes_192_cfb8(void);
const EVP_CIPHER *EVP_aes_192_cfb128(void);
const EVP_CIPHER *EVP_aes_192_ofb(void);
const EVP_CIPHER *EVP_aes_256_ecb(void);
const EVP_CIPHER *EVP_aes_256_cbc(void);
const EVP_CIPHER *EVP_aes_256_cfb1(void);
const EVP_CIPHER *EVP_aes_256_cfb8(void);
const EVP_CIPHER *EVP_aes_256_cfb128(void);
const EVP_CIPHER *EVP_aes_256_ofb(void);
DESCRIPTION
The EVP cipher routines are a high level interface to certain symmetric
ciphers.
EVP_CIPHER_CTX_init() initializes cipher contex ctx.
EVP_EncryptInit_ex() sets up cipher context ctx for encryption with
cipher type from ENGINE impl. ctx must be initialized before calling
this function. type is normally supplied by a function such as
EVP_aes_256_cbc(). If impl is NULL then the default implementation is
used. 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.
EVP_EncryptUpdate() 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 out should contain sufficient room. The
actual number of bytes written is placed in outl.
If padding is enabled (the default) then EVP_EncryptFinal_ex() encrypts
the "final" data, that is any data that remains in a partial block. It
uses standard block padding (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 outl. 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_ex() will not encrypt any
more data and it will 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_ex(), EVP_DecryptUpdate() and EVP_DecryptFinal_ex() are
the corresponding decryption operations. EVP_DecryptFinal() will 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 (inl + cipher_block_size) bytes unless the cipher
block size is 1 in which case inl bytes is sufficient.
EVP_CipherInit_ex(), EVP_CipherUpdate() 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_CIPHER_CTX_cleanup() clears all information from a cipher context
and free up any allocated memory associate with it. It should be called
after all operations using a cipher are complete so sensitive
information does not remain in memory.
EVP_EncryptInit(), EVP_DecryptInit() and EVP_CipherInit() behave in a
similar way to EVP_EncryptInit_ex(), EVP_DecryptInit_ex and
EVP_CipherInit_ex() except the ctx parameter does not need to be
initialized and they always use the default cipher implementation.
EVP_EncryptFinal(), EVP_DecryptFinal() and EVP_CipherFinal() are
identical to EVP_EncryptFinal_ex(), EVP_DecryptFinal_ex() and
EVP_CipherFinal_ex(). In previous releases they also cleaned up the
ctx, but this is no longer done and EVP_CIPHER_CTX_clean() must be
called to free any context resources.
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_nid() and EVP_CIPHER_CTX_nid() 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.
EVP_CIPHER_CTX_set_padding() enables or disables padding. By default
encryption operations are padded using standard block padding and the
padding is checked and removed when decrypting. If the pad parameter is
zero then no padding is performed, the total amount of data encrypted
or decrypted must then be a multiple of the block size or an error will
occur.
EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() 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. Note: although EVP_CIPHER_key_length() is fixed for a
given cipher, the value of EVP_CIPHER_CTX_key_length() may be different
for variable key length ciphers.
EVP_CIPHER_CTX_set_key_length() 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.
EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() 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.
EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() 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.
EVP_CIPHER_type() and EVP_CIPHER_CTX_type() 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.
EVP_CIPHER_CTX_cipher() returns the EVP_CIPHER structure when passed an
EVP_CIPHER_CTX structure.
EVP_CIPHER_mode() and EVP_CIPHER_CTX_mode() 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.
EVP_CIPHER_param_to_asn1() sets the AlgorithmIdentifier "parameter"
based on the passed cipher. This will typically 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(), EVP_DecryptUpdate() calls for example). This
function may fail if the cipher does not have any ASN1 support.
EVP_CIPHER_asn1_to_param() 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
EVP_CipherInit() will be called with the IV and key set to NULL,
EVP_CIPHER_asn1_to_param() will be called and finally EVP_CipherInit()
again with all parameters except the key 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.
EVP_CIPHER_CTX_ctrl() allows various cipher specific parameters to be
determined and set.
RETURN VALUES
EVP_EncryptInit_ex(), EVP_EncryptUpdate() and EVP_EncryptFinal_ex()
return 1 for success and 0 for failure.
EVP_DecryptInit_ex() and EVP_DecryptUpdate() return 1 for success and 0
for failure. EVP_DecryptFinal_ex() returns 0 if the decrypt failed or
1 for success.
EVP_CipherInit_ex() and EVP_CipherUpdate() return 1 for success and 0
for failure. EVP_CipherFinal_ex() returns 0 for a decryption failure
or 1 for success.
EVP_CIPHER_CTX_cleanup() returns 1 for success and 0 for failure.
EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj()
return an EVP_CIPHER structure or NULL on error.
EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return a NID.
EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the
block size.
EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key
length.
EVP_CIPHER_CTX_set_padding() always returns 1.
EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV
length or zero if the cipher does not use an IV.
EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the NID of the
cipher's OBJECT IDENTIFIER or NID_undef if it has no defined OBJECT
IDENTIFIER.
EVP_CIPHER_CTX_cipher() returns an EVP_CIPHER structure.
EVP_CIPHER_param_to_asn1() and EVP_CIPHER_asn1_to_param() return 1 for
success or zero for failure.
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_cbc(void), EVP_des_ede(), EVP_des_ede_ofb(void),
EVP_des_ede_cfb(void)
Two key triple DES in CBC, ECB, CFB and OFB modes respectively.
EVP_des_ede3_cbc(void), EVP_des_ede3(), EVP_des_ede3_ofb(void),
EVP_des_ede3_cfb(void)
Three key triple DES in CBC, ECB, CFB and OFB modes respectively.
EVP_desx_cbc(void)
DESX algorithm in CBC mode.
EVP_aes_128_cbc(void), EVP_aes_128_ecb(), EVP_aes_128_ofb(void),
EVP_aes_128_cfb1(void), EVP_aes_128_cfb8(void),
EVP_aes_128_cfb128(void)
AES with 128 bit key length in CBC, ECB, OFB and CFB modes
respectively.
EVP_aes_192_cbc(void), EVP_aes_192_ecb(), EVP_aes_192_ofb(void),
EVP_aes_192_cfb1(void), EVP_aes_192_cfb8(void),
EVP_aes_192_cfb128(void)
AES with 192 bit key length in CBC, ECB, OFB and CFB modes
respectively.
EVP_aes_256_cbc(void), EVP_aes_256_ecb(), EVP_aes_256_ofb(void),
EVP_aes_256_cfb1(void), EVP_aes_256_cfb8(void),
EVP_aes_256_cfb128(void)
AES with 256 bit key length in CBC, ECB, OFB and CFB modes
respectively.
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 EVP_rc4() and the EVP_CIPHER_CTX_set_key_length()
function.
EVP_idea_cbc() EVP_idea_ecb(void), EVP_idea_cfb(void),
EVP_idea_ofb(void), EVP_idea_cbc(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 EVP_rc2_cbc(), EVP_CIPHER_CTX_set_key_length() and
EVP_CIPHER_CTX_ctrl() 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_cbc(void), EVP_cast5_ecb(void), EVP_cast5_cfb(void),
EVP_cast5_ofb(void)
CAST encryption algorithm in CBC, ECB, CFB and OFB modes
respectively. This is a variable key length cipher.
EVP_rc5_32_12_16_cbc(void), EVP_rc5_32_12_16_ecb(void),
EVP_rc5_32_12_16_cfb(void), EVP_rc5_32_12_16_ofb(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.
EVP_aes_128_gcm(void), EVP_aes_192_gcm(void), EVP_aes_256_gcm(void)
AES Galois Counter Mode (GCM) for 128, 192 and 256 bit keys
respectively. These ciphers require additional control operations
to function correctly: see "GCM mode" section below for details.
EVP_aes_128_ccm(void), EVP_aes_192_ccm(void), EVP_aes_256_ccm(void)
AES Counter with CBC-MAC Mode (CCM) for 128, 192 and 256 bit keys
respectively. These ciphers require additional control operations
to function correctly: see CCM mode section below for details.
GCM Mode
For GCM mode ciphers the behaviour of the EVP interface is subtly
altered and several GCM specific ctrl operations are supported.
To specify any additional authenticated data (AAD) a call to
EVP_CipherUpdate(), EVP_EncryptUpdate() or EVP_DecryptUpdate() should
be made with the output parameter out set to NULL.
When decrypting the return value of EVP_DecryptFinal() or
EVP_CipherFinal() indicates if the operation was successful. If it does
not indicate success the authentication operation has failed and any
output data MUST NOT be used as it is corrupted.
The following ctrls are supported in GCM mode:
EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, ivlen, NULL);
Sets the GCM IV length: this call can only be made before specifying an
IV. If not called a default IV length is used (96 bits for AES).
EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, taglen, tag);
Writes taglen bytes of the tag value to the buffer indicated by tag.
This call can only be made when encrypting data and after all data has
been processed (e.g. after an EVP_EncryptFinal() call).
EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, taglen, tag);
Sets the expected tag to taglen bytes from tag. This call is only legal
when decrypting data and must be made before any data is processed
(e.g. before any EVP_DecryptUpdate() call).
See EXAMPLES below for an example of the use of GCM mode.
CCM Mode
The behaviour of CCM mode ciphers is similar to CCM mode but with a few
additional requirements and different ctrl values.
Like GCM mode any additional authenticated data (AAD) is passed by
calling EVP_CipherUpdate(), EVP_EncryptUpdate() or EVP_DecryptUpdate()
with the output parameter out set to NULL. Additionally the total
plaintext or ciphertext length MUST be passed to EVP_CipherUpdate(),
EVP_EncryptUpdate() or EVP_DecryptUpdate() with the output and input
parameters (in and out) set to NULL and the length passed in the inl
parameter.
The following ctrls are supported in CCM mode:
EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_TAG, taglen, tag);
This call is made to set the expected CCM tag value when decrypting or
the length of the tag (with the tag parameter set to NULL) when
encrypting. The tag length is often referred to as M. If not set a
default value is used (12 for AES).
EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_L, ivlen, NULL);
Sets the CCM L value. If not set a default is used (8 for AES).
EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_IVLEN, ivlen, NULL);
Sets the CCM nonce (IV) length: this call can only be made before
specifying an nonce value. The nonce length is given by 15 - L so it is
7 by default for AES.
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.
Additionally, the EVP interface will ensure the use of platform
specific cryptographic acceleration such as AES-NI (the low level
interfaces do not provide the guarantee).
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.
The functions EVP_EncryptInit(), EVP_EncryptFinal(), EVP_DecryptInit(),
EVP_CipherInit() and EVP_CipherFinal() are obsolete but are retained
for compatibility with existing code. New code should use
EVP_EncryptInit_ex(), EVP_EncryptFinal_ex(), EVP_DecryptInit_ex(),
EVP_DecryptFinal_ex(), EVP_CipherInit_ex() and EVP_CipherFinal_ex()
because they can reuse an existing context without allocating and
freeing it up on each call.
BUGS
For RC5 the number of rounds can currently only be set to 8, 12 or 16.
This is a limitation of the current RC5 code rather than the EVP
interface.
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.
EXAMPLES
Encrypt a string using IDEA:
int do_crypt(char *outfile)
{
unsigned char outbuf[1024];
int outlen, tmplen;
/* 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};
char intext[] = "Some Crypto Text";
EVP_CIPHER_CTX ctx;
FILE *out;
EVP_CIPHER_CTX_init(&ctx);
EVP_EncryptInit_ex(&ctx, EVP_idea_cbc(), NULL, key, iv);
if(!EVP_EncryptUpdate(&ctx, outbuf, &outlen, intext, strlen(intext)))
{
/* Error */
return 0;
}
/* Buffer passed to EVP_EncryptFinal() must be after data just
* encrypted to avoid overwriting it.
*/
if(!EVP_EncryptFinal_ex(&ctx, outbuf + outlen, &tmplen))
{
/* Error */
return 0;
}
outlen += tmplen;
EVP_CIPHER_CTX_cleanup(&ctx);
/* Need binary mode for fopen because encrypted data is
* binary data. Also cannot use strlen() on it because
* it wont be null terminated and may contain embedded
* nulls.
*/
out = fopen(outfile, "wb");
fwrite(outbuf, 1, outlen, out);
fclose(out);
return 1;
}
The ciphertext from the above example can be decrypted using the
openssl utility with the command line (shown on two lines for clarity):
openssl idea -d <filename
-K 000102030405060708090A0B0C0D0E0F -iv 0102030405060708
General encryption and decryption function example using FILE I/O and
AES128 with a 128-bit key:
int do_crypt(FILE *in, FILE *out, int do_encrypt)
{
/* Allow enough space in output buffer for additional block */
unsigned char inbuf[1024], outbuf[1024 + EVP_MAX_BLOCK_LENGTH];
int inlen, outlen;
EVP_CIPHER_CTX ctx;
/* Bogus key and IV: we'd normally set these from
* another source.
*/
unsigned char key[] = "0123456789abcdeF";
unsigned char iv[] = "1234567887654321";
/* Don't set key or IV right away; we want to check lengths */
EVP_CIPHER_CTX_init(&ctx);
EVP_CipherInit_ex(&ctx, EVP_aes_128_cbc(), NULL, NULL, NULL,
do_encrypt);
OPENSSL_assert(EVP_CIPHER_CTX_key_length(&ctx) == 16);
OPENSSL_assert(EVP_CIPHER_CTX_iv_length(&ctx) == 16);
/* Now we can set key and IV */
EVP_CipherInit_ex(&ctx, NULL, NULL, key, iv, do_encrypt);
for(;;)
{
inlen = fread(inbuf, 1, 1024, in);
if(inlen <= 0) break;
if(!EVP_CipherUpdate(&ctx, outbuf, &outlen, inbuf, inlen))
{
/* Error */
EVP_CIPHER_CTX_cleanup(&ctx);
return 0;
}
fwrite(outbuf, 1, outlen, out);
}
if(!EVP_CipherFinal_ex(&ctx, outbuf, &outlen))
{
/* Error */
EVP_CIPHER_CTX_cleanup(&ctx);
return 0;
}
fwrite(outbuf, 1, outlen, out);
EVP_CIPHER_CTX_cleanup(&ctx);
return 1;
}
SEE ALSO
evp(3)
HISTORY
EVP_CIPHER_CTX_init(), EVP_EncryptInit_ex(), EVP_EncryptFinal_ex(),
EVP_DecryptInit_ex(), EVP_DecryptFinal_ex(), EVP_CipherInit_ex(),
EVP_CipherFinal_ex() and EVP_CIPHER_CTX_set_padding() appeared in
OpenSSL 0.9.7.
IDEA appeared in OpenSSL 0.9.7 but was often disabled due to patent
concerns; the last patents expired in 2012.
1.0.2k 2023-11-13 EVP_EncryptInit(3)
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