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_rc4_hmac_md5,
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_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_aes_128_cbc_hmac_sha1, EVP_aes_256_cbc_hmac_sha1,
EVP_aes_128_cbc_hmac_sha256, EVP_aes_256_cbc_hmac_sha256 - 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);
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_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).
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.