EVP_CIPHER_CTX_set_padding(3)
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_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, const unsigned char *key, const unsigned char *iv);
int EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl, const unsigned char *in, int inl);
int EVP_EncryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl);
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
int EVP_DecryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
ENGINE *impl, const unsigned char *key, const unsigned char *iv);
int EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl, const 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, const unsigned char *key, const unsigned char *iv, int enc);
int EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl, const 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,
const unsigned char *key, const 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,
const unsigned char *key, const 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,
const unsigned char *key, const 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);
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
#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.
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
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.
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
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
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
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.
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
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_ofb(void)
EVP_des_cbc(void), EVP_des_ecb(void), EVP_des_cfb(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 EVP_rc4() and the
EVP_CIPHER_CTX_set_key_length() function.
EVP_idea_ofb(void), EVP_idea_cbc(void)
EVP_idea_cbc() EVP_idea_ecb(void), EVP_idea_cfb(void),
IDEA encryption algorithm in CBC, ECB, CFB and OFB modes
respectively.
EVP_rc2_ofb(void)
EVP_rc2_cbc(void), EVP_rc2_ecb(void), EVP_rc2_cfb(void),
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
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_ofb(void);
EVP_bf_cbc(void), EVP_bf_ecb(void), EVP_bf_cfb(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.
EVP_aes_256_gcm(void)
EVP_aes_128_gcm(void), EVP_aes_192_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_256_ccm(void)
EVP_aes_128_ccm(void), EVP_aes_192_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.
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
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.
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
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
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.
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
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);
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
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";
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EVP_EncryptInit(3) OpenSSL EVP_EncryptInit(3)
/* 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.
1.0.2t Last change: 2019-09-10 13
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