NAME
EVP_CIPHER_CTX_new
,
EVP_CIPHER_CTX_init
,
EVP_CIPHER_CTX_free
,
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_set_padding
,
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_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_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_aes_128_cbc
,
EVP_aes_128_ecb
,
EVP_aes_128_cfb
,
EVP_aes_128_ofb
,
EVP_aes_192_cbc
,
EVP_aes_192_ecb
,
EVP_aes_192_cfb
,
EVP_aes_192_ofb
,
EVP_aes_256_cbc
,
EVP_aes_256_ecb
,
EVP_aes_256_cfb
,
EVP_aes_256_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_rc5_32_12_16_cbc
,
EVP_rc5_32_12_16_cfb
,
EVP_rc5_32_12_16_ecb
,
EVP_rc5_32_12_16_ofb
,
EVP_chacha20
—
EVP cipher routines
SYNOPSIS
#include
<openssl/evp.h>
EVP_CIPHER_CTX *
EVP_CIPHER_CTX_new
(void);
void
EVP_CIPHER_CTX_init
(EVP_CIPHER_CTX
*ctx);
void
EVP_CIPHER_CTX_free
(EVP_CIPHER_CTX
*ctx);
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
*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);
int
EVP_CIPHER_nid
(const EVP_CIPHER
*e);
int
EVP_CIPHER_block_size
(const EVP_CIPHER
*e);
int
EVP_CIPHER_key_length
(const EVP_CIPHER
*e);
int
EVP_CIPHER_iv_length
(const EVP_CIPHER
*e);
unsigned long
EVP_CIPHER_flags
(const EVP_CIPHER
*e);
unsigned long
EVP_CIPHER_mode
(const EVP_CIPHER
*e);
int
EVP_CIPHER_type
(const EVP_CIPHER
*ctx);
const EVP_CIPHER *
EVP_CIPHER_CTX_cipher
(const
EVP_CIPHER_CTX *ctx);
int
EVP_CIPHER_CTX_nid
(const
EVP_CIPHER_CTX *ctx);
int
EVP_CIPHER_CTX_block_size
(const
EVP_CIPHER_CTX *ctx);
int
EVP_CIPHER_CTX_key_length
(const
EVP_CIPHER_CTX *ctx);
int
EVP_CIPHER_CTX_iv_length
(const
EVP_CIPHER_CTX *ctx);
void *
EVP_CIPHER_CTX_get_app_data
(const
EVP_CIPHER_CTX *ctx);
void
EVP_CIPHER_CTX_set_app_data
(const
EVP_CIPHER_CTX *ctx, void *data);
int
EVP_CIPHER_CTX_type
(const
EVP_CIPHER_CTX *ctx);
unsigned long
EVP_CIPHER_CTX_flags
(const
EVP_CIPHER_CTX *ctx);
unsigned long
EVP_CIPHER_CTX_mode
(const
EVP_CIPHER_CTX *ctx);
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.
EVP_CIPHER_CTX_new
()
creates a cipher context.
EVP_CIPHER_CTX_init
()
initializes the cipher context ctx.
EVP_CIPHER_CTX_free
()
clears all information from a cipher context and frees up any allocated
memory associate 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_EncryptInit_ex
()
sets up the 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 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
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 associated 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 of
OpenSSL, they also used to clean up the ctx, but this
is no longer done and EVP_CIPHER_CTX_cleanup
() 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. This function should be called after the
context is set up for encryption or decryption with
EVP_EncryptInit_ex
(),
EVP_DecryptInit_ex
(), or EVP_CipherInit_ex . By
default encryption operations are padded using standard block padding and
the padding is checked and removed when decrypting. If the
padding 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_BLOCK_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 ASN.1 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 ASN.1 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
() or
EVP_DecryptUpdate
() calls, for example). This
function may fail if the cipher does not have any ASN.1 support.
EVP_CIPHER_asn1_to_param
()
sets the cipher parameters based on an ASN.1
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 ASN.1 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.
Currently only the RC2 effective key length and the number of rounds of RC5
can be set.
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.
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.
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_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 greater than zero
for success and zero or a negative number for failure.
CIPHER LISTING
All algorithms have a fixed key length unless otherwise stated.
EVP_enc_null
()- Null cipher: does nothing.
EVP_aes_128_cbc
(),EVP_aes_128_ecb
(),EVP_aes_128_cfb
(),EVP_aes_128_ofb
()- AES with a 128-bit key in CBC, ECB, CFB and OFB modes respectively.
EVP_aes_192_cbc
(),EVP_aes_192_ecb
(),EVP_aes_192_cfb
(),EVP_aes_192_ofb
()- AES with a 192-bit key in CBC, ECB, CFB and OFB modes respectively.
EVP_aes_256_cbc
(),EVP_aes_256_ecb
(),EVP_aes_256_cfb
(),EVP_aes_256_ofb
()- AES with a 256-bit key in CBC, ECB, CFB and OFB modes respectively.
EVP_des_cbc
(),EVP_des_ecb
(),EVP_des_cfb
(),EVP_des_ofb
()- DES in CBC, ECB, CFB and OFB modes respectively.
EVP_des_ede_cbc
(),EVP_des_ede
(),EVP_des_ede_ofb
(),EVP_des_ede_cfb
()- Two key triple DES in CBC, ECB, CFB and OFB modes respectively.
EVP_des_ede3_cbc
(),EVP_des_ede3
(),EVP_des_ede3_ofb
(),EVP_des_ede3_cfb
()- Three key triple DES in CBC, ECB, CFB and OFB modes respectively.
EVP_desx_cbc
()- DESX algorithm in CBC mode.
EVP_rc4
()- RC4 stream cipher. This is a variable key length cipher with default key length 128 bits.
EVP_rc4_40
()- RC4 stream cipher with 40-bit key length. This is obsolete and new code
should use
EVP_rc4
() and theEVP_CIPHER_CTX_set_key_length
() function. EVP_idea_cbc
(),EVP_idea_ecb
(),EVP_idea_cfb
(),EVP_idea_ofb
()- IDEA encryption algorithm in CBC, ECB, CFB and OFB modes respectively.
EVP_rc2_cbc
(),EVP_rc2_ecb
(),EVP_rc2_cfb
(),EVP_rc2_ofb
()- 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
(),EVP_rc2_64_cbc
()- 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
(), andEVP_CIPHER_CTX_ctrl
() to set the key length and effective key length. EVP_bf_cbc
(),EVP_bf_ecb
(),EVP_bf_cfb
(),EVP_bf_ofb
()- Blowfish encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key length cipher.
EVP_cast5_cbc
(),EVP_cast5_ecb
(),EVP_cast5_cfb
(),EVP_cast5_ofb
()- CAST encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key length cipher.
EVP_rc5_32_12_16_cbc
(),EVP_rc5_32_12_16_ecb
(),EVP_rc5_32_12_16_cfb
(),EVP_rc5_32_12_16_ofb
()- 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
(),EVP_aes_192_gcm
(),EVP_aes_256_gcm
()- AES Galois Counter Mode (GCM) for 128, 192 and 256 bit keys respectively. These ciphers require additional control operations to function correctly: see the GCM mode section below for details.
EVP_aes_128_ccm
(),EVP_aes_192_ccm
(),EVP_aes_256_ccm
()- 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.
EVP_chacha20
()- The ChaCha20 stream cipher. The key length is 256 bits, the IV is 96 bits long.
GCM mode
For GCM mode ciphers, the behaviour of the EVP interface is subtly altered and several additional 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 IV length: this call can only be made before specifying an IV. If not called, a default IV length is used. For GCM AES the default is 12, i.e. 96 bits.
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.
CCM mode
The behaviour of CCM mode ciphers is similar to GCM 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.
EXAMPLES
Encrypt a string using blowfish:
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}; const char intext[] = "Some Crypto Text"; EVP_CIPHER_CTX ctx; FILE *out; EVP_CIPHER_CTX_init(&ctx); EVP_EncryptInit_ex(&ctx, EVP_bf_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 won't be NUL terminated and may contain embedded * NULs. */ 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(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 RC2 with an 80-bit key:
int do_crypt(FILE *in, FILE *out, int do_encrypt) { /* Allow enough space in output buffer for additional block */ inbuf[1024], outbuf[1024 + EVP_MAX_BLOCK_LENGTH]; int inlen, outlen; /* * Bogus key and IV: we'd normally set these from * another source. */ unsigned char key[] = "0123456789"; unsigned char iv[] = "12345678"; /* Don't set key or IV because we will modify the parameters */ EVP_CIPHER_CTX_init(&ctx); EVP_CipherInit_ex(&ctx, EVP_rc2(), NULL, NULL, NULL, do_encrypt); EVP_CIPHER_CTX_set_key_length(&ctx, 10); /* We finished modifying parameters so 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
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.
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 ASN.1 code is incomplete (and sometimes inaccurate). It has only been tested for certain common S/MIME ciphers (RC2, DES, triple DES) in CBC mode.