Index

openssl(1)

ssl(3)

crypto(3)

EVP_EncryptInit(3)

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
CIPHER LISTING
NOTES
BUGS
EXAMPLES
SEE ALSO
HISTORY

NAME

EVP_EncryptInit, EVP_EncryptUpdate, EVP_EncryptFinal - EVP cipher routines

SYNOPSIS

 #include <openssl/evp.h>

 int EVP_EncryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
         unsigned char *key, unsigned char *iv);
 int EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
         int *outl, unsigned char *in, int inl);
 int EVP_EncryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
         int *outl);

 int EVP_DecryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
         unsigned char *key, unsigned char *iv);
 int EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
         int *outl, unsigned char *in, int inl);
 int EVP_DecryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm,
         int *outl);

 int EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
         unsigned char *key, unsigned char *iv, int enc);
 int EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
         int *outl, unsigned char *in, int inl);
 int EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm,
         int *outl);

 int EVP_CIPHER_CTX_set_key_length(EVP_CIPHER_CTX *x, int keylen);
 int EVP_CIPHER_CTX_ctrl(EVP_CIPHER_CTX *ctx, int type, int arg, void *ptr);
 int EVP_CIPHER_CTX_cleanup(EVP_CIPHER_CTX *a);

 const EVP_CIPHER *EVP_get_cipherbyname(const char *name);
 #define EVP_get_cipherbynid(a) EVP_get_cipherbyname(OBJ_nid2sn(a))
 #define EVP_get_cipherbyobj(a) EVP_get_cipherbynid(OBJ_obj2nid(a))

 #define EVP_CIPHER_nid(e)              ((e)->nid)
 #define EVP_CIPHER_block_size(e)       ((e)->block_size)
 #define EVP_CIPHER_key_length(e)       ((e)->key_len)
 #define EVP_CIPHER_iv_length(e)                ((e)->iv_len)
 #define EVP_CIPHER_flags(e)            ((e)->flags)
 #define EVP_CIPHER_mode(e)             ((e)->flags) & EVP_CIPH_MODE)
 int EVP_CIPHER_type(const EVP_CIPHER *ctx);

 #define EVP_CIPHER_CTX_cipher(e)       ((e)->cipher)
 #define EVP_CIPHER_CTX_nid(e)          ((e)->cipher->nid)
 #define EVP_CIPHER_CTX_block_size(e)   ((e)->cipher->block_size)
 #define EVP_CIPHER_CTX_key_length(e)   ((e)->key_len)
 #define EVP_CIPHER_CTX_iv_length(e)    ((e)->cipher->iv_len)
 #define EVP_CIPHER_CTX_get_app_data(e) ((e)->app_data)
 #define EVP_CIPHER_CTX_set_app_data(e,d) ((e)->app_data=(char *)(d))
 #define EVP_CIPHER_CTX_type(c)         EVP_CIPHER_type(EVP_CIPHER_CTX_cipher(c))
 #define EVP_CIPHER_CTX_flags(e)                ((e)->cipher->flags)
 #define EVP_CIPHER_CTX_mode(e)         ((e)->cipher->flags & EVP_CIPH_MODE)

 int EVP_CIPHER_param_to_asn1(EVP_CIPHER_CTX *c, ASN1_TYPE *type);
 int EVP_CIPHER_asn1_to_param(EVP_CIPHER_CTX *c, ASN1_TYPE *type);

DESCRIPTION

The EVP cipher routines are a high level interface to certain symmetric ciphers.

EVP_EncryptInit() initialises a cipher context ctx for encryption with cipher type. type is normally supplied by a function such as EVP_des_cbc() . 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 outl should contain sufficient room. The actual number of bytes written is placed in outl.

EVP_EncryptFinal() 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.

EVP_DecryptInit(), EVP_DecryptUpdate() and EVP_DecryptFinal() are the corresponding decryption operations. EVP_DecryptFinal() will return an error code if the final block is not correctly formatted. The parameters and restrictions are identical to the encryption operations except that the decrypted data buffer out passed to EVP_DecryptUpdate() should have sufficient room for (inl + cipher_block_size) bytes unless the cipher block size is 1 in which case inl bytes is sufficient.

EVP_CipherInit(), EVP_CipherUpdate() and EVP_CipherFinal() 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. It should be called after all operations using a cipher are complete so sensitive information does not remain in memory.

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_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. Currently only the RC2 effective key length and the number of rounds of RC5 can be set.

RETURN VALUES

EVP_EncryptInit(), EVP_EncryptUpdate() and EVP_EncryptFinal() return 1 for success and 0 for failure.

EVP_DecryptInit() and EVP_DecryptUpdate() return 1 for success and 0 for failure. EVP_DecryptFinal() returns 0 if the decrypt failed or 1 for success.

EVP_CipherInit() and EVP_CipherUpdate() return 1 for success and 0 for failure. EVP_CipherFinal() returns 1 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_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): IDES encryption algorothm 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.

NOTES

Where possible the EVP interface to symmetric ciphers should be used in preference to the low level interfaces. This is because the code then becomes transparent to the cipher used and much more flexible.

PKCS padding works by adding n padding bytes of value n to make the total length of the encrypted data a multiple of the block size. 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, 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.

The functions EVP_EncryptInit(), EVP_EncryptUpdate(), EVP_EncryptFinal(), EVP_DecryptInit(), EVP_DecryptUpdate(), EVP_CipherInit() and EVP_CipherUpdate() and EVP_CIPHER_CTX_cleanup() did not return errors in OpenSSL version 0.9.5a or earlier. Software only versions of encryption algorithms will never return error codes for these functions, unless there is a programming error (for example and attempt to set the key before the cipher is set in EVP_EncryptInit() ).

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.

It should be possible to disable PKCS padding: currently it isn't.

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 innacurate) it has only been tested for certain common S/MIME ciphers (RC2, DES, triple DES) in CBC mode.

EXAMPLES

Get the number of rounds used in RC5:

 int nrounds;
 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GET_RC5_ROUNDS, 0, &i);

Get the RC2 effective key length:

 int key_bits;
 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GET_RC2_KEY_BITS, 0, &i);

Set the number of rounds used in RC5:

 int nrounds;
 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_SET_RC5_ROUNDS, i, NULL);

Set the number of rounds used in RC2:

 int nrounds;
 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_SET_RC2_KEY_BITS, i, NULL);