EVP_EncryptInit.pod revision 325335
1=pod 2 3=head1 NAME 4 5EVP_CIPHER_CTX_init, EVP_EncryptInit_ex, EVP_EncryptUpdate, 6EVP_EncryptFinal_ex, EVP_DecryptInit_ex, EVP_DecryptUpdate, 7EVP_DecryptFinal_ex, EVP_CipherInit_ex, EVP_CipherUpdate, 8EVP_CipherFinal_ex, EVP_CIPHER_CTX_set_key_length, 9EVP_CIPHER_CTX_ctrl, EVP_CIPHER_CTX_cleanup, EVP_EncryptInit, 10EVP_EncryptFinal, EVP_DecryptInit, EVP_DecryptFinal, 11EVP_CipherInit, EVP_CipherFinal, EVP_get_cipherbyname, 12EVP_get_cipherbynid, EVP_get_cipherbyobj, EVP_CIPHER_nid, 13EVP_CIPHER_block_size, EVP_CIPHER_key_length, EVP_CIPHER_iv_length, 14EVP_CIPHER_flags, EVP_CIPHER_mode, EVP_CIPHER_type, EVP_CIPHER_CTX_cipher, 15EVP_CIPHER_CTX_nid, EVP_CIPHER_CTX_block_size, EVP_CIPHER_CTX_key_length, 16EVP_CIPHER_CTX_iv_length, EVP_CIPHER_CTX_get_app_data, 17EVP_CIPHER_CTX_set_app_data, EVP_CIPHER_CTX_type, EVP_CIPHER_CTX_flags, 18EVP_CIPHER_CTX_mode, EVP_CIPHER_param_to_asn1, EVP_CIPHER_asn1_to_param, 19EVP_CIPHER_CTX_set_padding, EVP_enc_null, EVP_des_cbc, EVP_des_ecb, 20EVP_des_cfb, EVP_des_ofb, EVP_des_ede_cbc, EVP_des_ede, EVP_des_ede_ofb, 21EVP_des_ede_cfb, EVP_des_ede3_cbc, EVP_des_ede3, EVP_des_ede3_ofb, 22EVP_des_ede3_cfb, EVP_desx_cbc, EVP_rc4, EVP_rc4_40, EVP_rc4_hmac_md5, 23EVP_idea_cbc, EVP_idea_ecb, EVP_idea_cfb, EVP_idea_ofb, EVP_rc2_cbc, 24EVP_rc2_ecb, EVP_rc2_cfb, EVP_rc2_ofb, EVP_rc2_40_cbc, EVP_rc2_64_cbc, 25EVP_bf_cbc, EVP_bf_ecb, EVP_bf_cfb, EVP_bf_ofb, EVP_cast5_cbc, 26EVP_cast5_ecb, EVP_cast5_cfb, EVP_cast5_ofb, EVP_rc5_32_12_16_cbc, 27EVP_rc5_32_12_16_ecb, EVP_rc5_32_12_16_cfb, EVP_rc5_32_12_16_ofb, 28EVP_aes_128_gcm, EVP_aes_192_gcm, EVP_aes_256_gcm, EVP_aes_128_ccm, 29EVP_aes_192_ccm, EVP_aes_256_ccm, 30EVP_aes_128_cbc_hmac_sha1, EVP_aes_256_cbc_hmac_sha1, 31EVP_aes_128_cbc_hmac_sha256, EVP_aes_256_cbc_hmac_sha256 32- EVP cipher routines 33 34=head1 SYNOPSIS 35 36 #include <openssl/evp.h> 37 38 void EVP_CIPHER_CTX_init(EVP_CIPHER_CTX *a); 39 40 int EVP_EncryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 41 ENGINE *impl, unsigned char *key, unsigned char *iv); 42 int EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, 43 int *outl, unsigned char *in, int inl); 44 int EVP_EncryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *out, 45 int *outl); 46 47 int EVP_DecryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 48 ENGINE *impl, unsigned char *key, unsigned char *iv); 49 int EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, 50 int *outl, unsigned char *in, int inl); 51 int EVP_DecryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm, 52 int *outl); 53 54 int EVP_CipherInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 55 ENGINE *impl, unsigned char *key, unsigned char *iv, int enc); 56 int EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, 57 int *outl, unsigned char *in, int inl); 58 int EVP_CipherFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm, 59 int *outl); 60 61 int EVP_EncryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 62 unsigned char *key, unsigned char *iv); 63 int EVP_EncryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, 64 int *outl); 65 66 int EVP_DecryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 67 unsigned char *key, unsigned char *iv); 68 int EVP_DecryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, 69 int *outl); 70 71 int EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 72 unsigned char *key, unsigned char *iv, int enc); 73 int EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, 74 int *outl); 75 76 int EVP_CIPHER_CTX_set_padding(EVP_CIPHER_CTX *x, int padding); 77 int EVP_CIPHER_CTX_set_key_length(EVP_CIPHER_CTX *x, int keylen); 78 int EVP_CIPHER_CTX_ctrl(EVP_CIPHER_CTX *ctx, int type, int arg, void *ptr); 79 int EVP_CIPHER_CTX_cleanup(EVP_CIPHER_CTX *a); 80 81 const EVP_CIPHER *EVP_get_cipherbyname(const char *name); 82 #define EVP_get_cipherbynid(a) EVP_get_cipherbyname(OBJ_nid2sn(a)) 83 #define EVP_get_cipherbyobj(a) EVP_get_cipherbynid(OBJ_obj2nid(a)) 84 85 #define EVP_CIPHER_nid(e) ((e)->nid) 86 #define EVP_CIPHER_block_size(e) ((e)->block_size) 87 #define EVP_CIPHER_key_length(e) ((e)->key_len) 88 #define EVP_CIPHER_iv_length(e) ((e)->iv_len) 89 #define EVP_CIPHER_flags(e) ((e)->flags) 90 #define EVP_CIPHER_mode(e) ((e)->flags) & EVP_CIPH_MODE) 91 int EVP_CIPHER_type(const EVP_CIPHER *ctx); 92 93 #define EVP_CIPHER_CTX_cipher(e) ((e)->cipher) 94 #define EVP_CIPHER_CTX_nid(e) ((e)->cipher->nid) 95 #define EVP_CIPHER_CTX_block_size(e) ((e)->cipher->block_size) 96 #define EVP_CIPHER_CTX_key_length(e) ((e)->key_len) 97 #define EVP_CIPHER_CTX_iv_length(e) ((e)->cipher->iv_len) 98 #define EVP_CIPHER_CTX_get_app_data(e) ((e)->app_data) 99 #define EVP_CIPHER_CTX_set_app_data(e,d) ((e)->app_data=(char *)(d)) 100 #define EVP_CIPHER_CTX_type(c) EVP_CIPHER_type(EVP_CIPHER_CTX_cipher(c)) 101 #define EVP_CIPHER_CTX_flags(e) ((e)->cipher->flags) 102 #define EVP_CIPHER_CTX_mode(e) ((e)->cipher->flags & EVP_CIPH_MODE) 103 104 int EVP_CIPHER_param_to_asn1(EVP_CIPHER_CTX *c, ASN1_TYPE *type); 105 int EVP_CIPHER_asn1_to_param(EVP_CIPHER_CTX *c, ASN1_TYPE *type); 106 107=head1 DESCRIPTION 108 109The EVP cipher routines are a high level interface to certain 110symmetric ciphers. 111 112EVP_CIPHER_CTX_init() initializes cipher contex B<ctx>. 113 114EVP_EncryptInit_ex() sets up cipher context B<ctx> for encryption 115with cipher B<type> from ENGINE B<impl>. B<ctx> must be initialized 116before calling this function. B<type> is normally supplied 117by a function such as EVP_aes_256_cbc(). If B<impl> is NULL then the 118default implementation is used. B<key> is the symmetric key to use 119and B<iv> is the IV to use (if necessary), the actual number of bytes 120used for the key and IV depends on the cipher. It is possible to set 121all parameters to NULL except B<type> in an initial call and supply 122the remaining parameters in subsequent calls, all of which have B<type> 123set to NULL. This is done when the default cipher parameters are not 124appropriate. 125 126EVP_EncryptUpdate() encrypts B<inl> bytes from the buffer B<in> and 127writes the encrypted version to B<out>. This function can be called 128multiple times to encrypt successive blocks of data. The amount 129of data written depends on the block alignment of the encrypted data: 130as a result the amount of data written may be anything from zero bytes 131to (inl + cipher_block_size - 1) so B<out> should contain sufficient 132room. The actual number of bytes written is placed in B<outl>. 133 134If padding is enabled (the default) then EVP_EncryptFinal_ex() encrypts 135the "final" data, that is any data that remains in a partial block. 136It uses L<standard block padding|/NOTES> (aka PKCS padding). The encrypted 137final data is written to B<out> which should have sufficient space for 138one cipher block. The number of bytes written is placed in B<outl>. After 139this function is called the encryption operation is finished and no further 140calls to EVP_EncryptUpdate() should be made. 141 142If padding is disabled then EVP_EncryptFinal_ex() will not encrypt any more 143data and it will return an error if any data remains in a partial block: 144that is if the total data length is not a multiple of the block size. 145 146EVP_DecryptInit_ex(), EVP_DecryptUpdate() and EVP_DecryptFinal_ex() are the 147corresponding decryption operations. EVP_DecryptFinal() will return an 148error code if padding is enabled and the final block is not correctly 149formatted. The parameters and restrictions are identical to the encryption 150operations except that if padding is enabled the decrypted data buffer B<out> 151passed to EVP_DecryptUpdate() should have sufficient room for 152(B<inl> + cipher_block_size) bytes unless the cipher block size is 1 in 153which case B<inl> bytes is sufficient. 154 155EVP_CipherInit_ex(), EVP_CipherUpdate() and EVP_CipherFinal_ex() are 156functions that can be used for decryption or encryption. The operation 157performed depends on the value of the B<enc> parameter. It should be set 158to 1 for encryption, 0 for decryption and -1 to leave the value unchanged 159(the actual value of 'enc' being supplied in a previous call). 160 161EVP_CIPHER_CTX_cleanup() clears all information from a cipher context 162and free up any allocated memory associate with it. It should be called 163after all operations using a cipher are complete so sensitive information 164does not remain in memory. 165 166EVP_EncryptInit(), EVP_DecryptInit() and EVP_CipherInit() behave in a 167similar way to EVP_EncryptInit_ex(), EVP_DecryptInit_ex and 168EVP_CipherInit_ex() except the B<ctx> parameter does not need to be 169initialized and they always use the default cipher implementation. 170 171EVP_EncryptFinal(), EVP_DecryptFinal() and EVP_CipherFinal() are 172identical to EVP_EncryptFinal_ex(), EVP_DecryptFinal_ex() and 173EVP_CipherFinal_ex(). In previous releases they also cleaned up 174the B<ctx>, but this is no longer done and EVP_CIPHER_CTX_clean() 175must be called to free any context resources. 176 177EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj() 178return an EVP_CIPHER structure when passed a cipher name, a NID or an 179ASN1_OBJECT structure. 180 181EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return the NID of a cipher when 182passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> structure. The actual NID 183value is an internal value which may not have a corresponding OBJECT 184IDENTIFIER. 185 186EVP_CIPHER_CTX_set_padding() enables or disables padding. By default 187encryption operations are padded using standard block padding and the 188padding is checked and removed when decrypting. If the B<pad> parameter 189is zero then no padding is performed, the total amount of data encrypted 190or decrypted must then be a multiple of the block size or an error will 191occur. 192 193EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key 194length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> 195structure. The constant B<EVP_MAX_KEY_LENGTH> is the maximum key length 196for all ciphers. Note: although EVP_CIPHER_key_length() is fixed for a 197given cipher, the value of EVP_CIPHER_CTX_key_length() may be different 198for variable key length ciphers. 199 200EVP_CIPHER_CTX_set_key_length() sets the key length of the cipher ctx. 201If the cipher is a fixed length cipher then attempting to set the key 202length to any value other than the fixed value is an error. 203 204EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV 205length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>. 206It will return zero if the cipher does not use an IV. The constant 207B<EVP_MAX_IV_LENGTH> is the maximum IV length for all ciphers. 208 209EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block 210size of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> 211structure. The constant B<EVP_MAX_IV_LENGTH> is also the maximum block 212length for all ciphers. 213 214EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the type of the passed 215cipher or context. This "type" is the actual NID of the cipher OBJECT 216IDENTIFIER as such it ignores the cipher parameters and 40 bit RC2 and 217128 bit RC2 have the same NID. If the cipher does not have an object 218identifier or does not have ASN1 support this function will return 219B<NID_undef>. 220 221EVP_CIPHER_CTX_cipher() returns the B<EVP_CIPHER> structure when passed 222an B<EVP_CIPHER_CTX> structure. 223 224EVP_CIPHER_mode() and EVP_CIPHER_CTX_mode() return the block cipher mode: 225EVP_CIPH_ECB_MODE, EVP_CIPH_CBC_MODE, EVP_CIPH_CFB_MODE or 226EVP_CIPH_OFB_MODE. If the cipher is a stream cipher then 227EVP_CIPH_STREAM_CIPHER is returned. 228 229EVP_CIPHER_param_to_asn1() sets the AlgorithmIdentifier "parameter" based 230on the passed cipher. This will typically include any parameters and an 231IV. The cipher IV (if any) must be set when this call is made. This call 232should be made before the cipher is actually "used" (before any 233EVP_EncryptUpdate(), EVP_DecryptUpdate() calls for example). This function 234may fail if the cipher does not have any ASN1 support. 235 236EVP_CIPHER_asn1_to_param() sets the cipher parameters based on an ASN1 237AlgorithmIdentifier "parameter". The precise effect depends on the cipher 238In the case of RC2, for example, it will set the IV and effective key length. 239This function should be called after the base cipher type is set but before 240the key is set. For example EVP_CipherInit() will be called with the IV and 241key set to NULL, EVP_CIPHER_asn1_to_param() will be called and finally 242EVP_CipherInit() again with all parameters except the key set to NULL. It is 243possible for this function to fail if the cipher does not have any ASN1 support 244or the parameters cannot be set (for example the RC2 effective key length 245is not supported. 246 247EVP_CIPHER_CTX_ctrl() allows various cipher specific parameters to be determined 248and set. 249 250=head1 RETURN VALUES 251 252EVP_EncryptInit_ex(), EVP_EncryptUpdate() and EVP_EncryptFinal_ex() 253return 1 for success and 0 for failure. 254 255EVP_DecryptInit_ex() and EVP_DecryptUpdate() return 1 for success and 0 for failure. 256EVP_DecryptFinal_ex() returns 0 if the decrypt failed or 1 for success. 257 258EVP_CipherInit_ex() and EVP_CipherUpdate() return 1 for success and 0 for failure. 259EVP_CipherFinal_ex() returns 0 for a decryption failure or 1 for success. 260 261EVP_CIPHER_CTX_cleanup() returns 1 for success and 0 for failure. 262 263EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj() 264return an B<EVP_CIPHER> structure or NULL on error. 265 266EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return a NID. 267 268EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block 269size. 270 271EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key 272length. 273 274EVP_CIPHER_CTX_set_padding() always returns 1. 275 276EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV 277length or zero if the cipher does not use an IV. 278 279EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the NID of the cipher's 280OBJECT IDENTIFIER or NID_undef if it has no defined OBJECT IDENTIFIER. 281 282EVP_CIPHER_CTX_cipher() returns an B<EVP_CIPHER> structure. 283 284EVP_CIPHER_param_to_asn1() and EVP_CIPHER_asn1_to_param() return 1 for 285success or zero for failure. 286 287=head1 CIPHER LISTING 288 289All algorithms have a fixed key length unless otherwise stated. 290 291=over 4 292 293=item EVP_enc_null() 294 295Null cipher: does nothing. 296 297=item EVP_des_cbc(void), EVP_des_ecb(void), EVP_des_cfb(void), EVP_des_ofb(void) 298 299DES in CBC, ECB, CFB and OFB modes respectively. 300 301=item EVP_des_ede_cbc(void), EVP_des_ede(), EVP_des_ede_ofb(void), EVP_des_ede_cfb(void) 302 303Two key triple DES in CBC, ECB, CFB and OFB modes respectively. 304 305=item EVP_des_ede3_cbc(void), EVP_des_ede3(), EVP_des_ede3_ofb(void), EVP_des_ede3_cfb(void) 306 307Three key triple DES in CBC, ECB, CFB and OFB modes respectively. 308 309=item EVP_desx_cbc(void) 310 311DESX algorithm in CBC mode. 312 313=item EVP_rc4(void) 314 315RC4 stream cipher. This is a variable key length cipher with default key length 128 bits. 316 317=item EVP_rc4_40(void) 318 319RC4 stream cipher with 40 bit key length. This is obsolete and new code should use EVP_rc4() 320and the EVP_CIPHER_CTX_set_key_length() function. 321 322=item EVP_idea_cbc() EVP_idea_ecb(void), EVP_idea_cfb(void), EVP_idea_ofb(void) 323 324IDEA encryption algorithm in CBC, ECB, CFB and OFB modes respectively. 325 326=item EVP_rc2_cbc(void), EVP_rc2_ecb(void), EVP_rc2_cfb(void), EVP_rc2_ofb(void) 327 328RC2 encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key 329length cipher with an additional parameter called "effective key bits" or "effective key length". 330By default both are set to 128 bits. 331 332=item EVP_rc2_40_cbc(void), EVP_rc2_64_cbc(void) 333 334RC2 algorithm in CBC mode with a default key length and effective key length of 40 and 64 bits. 335These are obsolete and new code should use EVP_rc2_cbc(), EVP_CIPHER_CTX_set_key_length() and 336EVP_CIPHER_CTX_ctrl() to set the key length and effective key length. 337 338=item EVP_bf_cbc(void), EVP_bf_ecb(void), EVP_bf_cfb(void), EVP_bf_ofb(void); 339 340Blowfish encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key 341length cipher. 342 343=item EVP_cast5_cbc(void), EVP_cast5_ecb(void), EVP_cast5_cfb(void), EVP_cast5_ofb(void) 344 345CAST encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key 346length cipher. 347 348=item 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) 349 350RC5 encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key length 351cipher with an additional "number of rounds" parameter. By default the key length is set to 128 352bits and 12 rounds. 353 354=item EVP_aes_128_gcm(void), EVP_aes_192_gcm(void), EVP_aes_256_gcm(void) 355 356AES Galois Counter Mode (GCM) for 128, 192 and 256 bit keys respectively. 357These ciphers require additional control operations to function correctly: see 358L<GCM mode> section below for details. 359 360=item EVP_aes_128_ccm(void), EVP_aes_192_ccm(void), EVP_aes_256_ccm(void) 361 362AES Counter with CBC-MAC Mode (CCM) for 128, 192 and 256 bit keys respectively. 363These ciphers require additional control operations to function correctly: see 364CCM mode section below for details. 365 366=back 367 368=head1 GCM Mode 369 370For GCM mode ciphers the behaviour of the EVP interface is subtly altered and 371several GCM specific ctrl operations are supported. 372 373To specify any additional authenticated data (AAD) a call to EVP_CipherUpdate(), 374EVP_EncryptUpdate() or EVP_DecryptUpdate() should be made with the output 375parameter B<out> set to B<NULL>. 376 377When decrypting the return value of EVP_DecryptFinal() or EVP_CipherFinal() 378indicates if the operation was successful. If it does not indicate success 379the authentication operation has failed and any output data B<MUST NOT> 380be used as it is corrupted. 381 382The following ctrls are supported in GCM mode: 383 384 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, ivlen, NULL); 385 386Sets the GCM IV length: this call can only be made before specifying an IV. If 387not called a default IV length is used (96 bits for AES). 388 389 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, taglen, tag); 390 391Writes B<taglen> bytes of the tag value to the buffer indicated by B<tag>. 392This call can only be made when encrypting data and B<after> all data has been 393processed (e.g. after an EVP_EncryptFinal() call). 394 395 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, taglen, tag); 396 397Sets the expected tag to B<taglen> bytes from B<tag>. This call is only legal 398when decrypting data and must be made B<before> any data is processed (e.g. 399before any EVP_DecryptUpdate() call). 400 401=head1 CCM Mode 402 403The behaviour of CCM mode ciphers is similar to CCM mode but with a few 404additional requirements and different ctrl values. 405 406Like GCM mode any additional authenticated data (AAD) is passed by calling 407EVP_CipherUpdate(), EVP_EncryptUpdate() or EVP_DecryptUpdate() with the output 408parameter B<out> set to B<NULL>. Additionally the total plaintext or ciphertext 409length B<MUST> be passed to EVP_CipherUpdate(), EVP_EncryptUpdate() or 410EVP_DecryptUpdate() with the output and input parameters (B<in> and B<out>) 411set to B<NULL> and the length passed in the B<inl> parameter. 412 413The following ctrls are supported in CCM mode: 414 415 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_TAG, taglen, tag); 416 417This call is made to set the expected B<CCM> tag value when decrypting or 418the length of the tag (with the B<tag> parameter set to NULL) when encrypting. 419The tag length is often referred to as B<M>. If not set a default value is 420used (12 for AES). 421 422 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_L, ivlen, NULL); 423 424Sets the CCM B<L> value. If not set a default is used (8 for AES). 425 426 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_IVLEN, ivlen, NULL); 427 428Sets the CCM nonce (IV) length: this call can only be made before specifying 429an nonce value. The nonce length is given by B<15 - L> so it is 7 by default 430for AES. 431 432 433 434=head1 NOTES 435 436Where possible the B<EVP> interface to symmetric ciphers should be used in 437preference to the low level interfaces. This is because the code then becomes 438transparent to the cipher used and much more flexible. Additionally, the 439B<EVP> interface will ensure the use of platform specific cryptographic 440acceleration such as AES-NI (the low level interfaces do not provide the 441guarantee). 442 443PKCS padding works by adding B<n> padding bytes of value B<n> to make the total 444length of the encrypted data a multiple of the block size. Padding is always 445added so if the data is already a multiple of the block size B<n> will equal 446the block size. For example if the block size is 8 and 11 bytes are to be 447encrypted then 5 padding bytes of value 5 will be added. 448 449When decrypting the final block is checked to see if it has the correct form. 450 451Although the decryption operation can produce an error if padding is enabled, 452it is not a strong test that the input data or key is correct. A random block 453has better than 1 in 256 chance of being of the correct format and problems with 454the input data earlier on will not produce a final decrypt error. 455 456If padding is disabled then the decryption operation will always succeed if 457the total amount of data decrypted is a multiple of the block size. 458 459The functions EVP_EncryptInit(), EVP_EncryptFinal(), EVP_DecryptInit(), 460EVP_CipherInit() and EVP_CipherFinal() are obsolete but are retained for 461compatibility with existing code. New code should use EVP_EncryptInit_ex(), 462EVP_EncryptFinal_ex(), EVP_DecryptInit_ex(), EVP_DecryptFinal_ex(), 463EVP_CipherInit_ex() and EVP_CipherFinal_ex() because they can reuse an 464existing context without allocating and freeing it up on each call. 465 466=head1 BUGS 467 468For RC5 the number of rounds can currently only be set to 8, 12 or 16. This is 469a limitation of the current RC5 code rather than the EVP interface. 470 471EVP_MAX_KEY_LENGTH and EVP_MAX_IV_LENGTH only refer to the internal ciphers with 472default key lengths. If custom ciphers exceed these values the results are 473unpredictable. This is because it has become standard practice to define a 474generic key as a fixed unsigned char array containing EVP_MAX_KEY_LENGTH bytes. 475 476The ASN1 code is incomplete (and sometimes inaccurate) it has only been tested 477for certain common S/MIME ciphers (RC2, DES, triple DES) in CBC mode. 478 479=head1 EXAMPLES 480 481Encrypt a string using IDEA: 482 483 int do_crypt(char *outfile) 484 { 485 unsigned char outbuf[1024]; 486 int outlen, tmplen; 487 /* Bogus key and IV: we'd normally set these from 488 * another source. 489 */ 490 unsigned char key[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}; 491 unsigned char iv[] = {1,2,3,4,5,6,7,8}; 492 char intext[] = "Some Crypto Text"; 493 EVP_CIPHER_CTX ctx; 494 FILE *out; 495 496 EVP_CIPHER_CTX_init(&ctx); 497 EVP_EncryptInit_ex(&ctx, EVP_idea_cbc(), NULL, key, iv); 498 499 if(!EVP_EncryptUpdate(&ctx, outbuf, &outlen, intext, strlen(intext))) 500 { 501 /* Error */ 502 return 0; 503 } 504 /* Buffer passed to EVP_EncryptFinal() must be after data just 505 * encrypted to avoid overwriting it. 506 */ 507 if(!EVP_EncryptFinal_ex(&ctx, outbuf + outlen, &tmplen)) 508 { 509 /* Error */ 510 return 0; 511 } 512 outlen += tmplen; 513 EVP_CIPHER_CTX_cleanup(&ctx); 514 /* Need binary mode for fopen because encrypted data is 515 * binary data. Also cannot use strlen() on it because 516 * it wont be null terminated and may contain embedded 517 * nulls. 518 */ 519 out = fopen(outfile, "wb"); 520 fwrite(outbuf, 1, outlen, out); 521 fclose(out); 522 return 1; 523 } 524 525The ciphertext from the above example can be decrypted using the B<openssl> 526utility with the command line (shown on two lines for clarity): 527 528 openssl idea -d <filename 529 -K 000102030405060708090A0B0C0D0E0F -iv 0102030405060708 530 531General encryption and decryption function example using FILE I/O and AES128 532with a 128-bit key: 533 534 int do_crypt(FILE *in, FILE *out, int do_encrypt) 535 { 536 /* Allow enough space in output buffer for additional block */ 537 unsigned char inbuf[1024], outbuf[1024 + EVP_MAX_BLOCK_LENGTH]; 538 int inlen, outlen; 539 EVP_CIPHER_CTX ctx; 540 /* Bogus key and IV: we'd normally set these from 541 * another source. 542 */ 543 unsigned char key[] = "0123456789abcdeF"; 544 unsigned char iv[] = "1234567887654321"; 545 546 /* Don't set key or IV right away; we want to check lengths */ 547 EVP_CIPHER_CTX_init(&ctx); 548 EVP_CipherInit_ex(&ctx, EVP_aes_128_cbc(), NULL, NULL, NULL, 549 do_encrypt); 550 OPENSSL_assert(EVP_CIPHER_CTX_key_length(&ctx) == 16); 551 OPENSSL_assert(EVP_CIPHER_CTX_iv_length(&ctx) == 16); 552 553 /* Now we can set key and IV */ 554 EVP_CipherInit_ex(&ctx, NULL, NULL, key, iv, do_encrypt); 555 556 for(;;) 557 { 558 inlen = fread(inbuf, 1, 1024, in); 559 if(inlen <= 0) break; 560 if(!EVP_CipherUpdate(&ctx, outbuf, &outlen, inbuf, inlen)) 561 { 562 /* Error */ 563 EVP_CIPHER_CTX_cleanup(&ctx); 564 return 0; 565 } 566 fwrite(outbuf, 1, outlen, out); 567 } 568 if(!EVP_CipherFinal_ex(&ctx, outbuf, &outlen)) 569 { 570 /* Error */ 571 EVP_CIPHER_CTX_cleanup(&ctx); 572 return 0; 573 } 574 fwrite(outbuf, 1, outlen, out); 575 576 EVP_CIPHER_CTX_cleanup(&ctx); 577 return 1; 578 } 579 580 581=head1 SEE ALSO 582 583L<evp(3)|evp(3)> 584 585=head1 HISTORY 586 587EVP_CIPHER_CTX_init(), EVP_EncryptInit_ex(), EVP_EncryptFinal_ex(), 588EVP_DecryptInit_ex(), EVP_DecryptFinal_ex(), EVP_CipherInit_ex(), 589EVP_CipherFinal_ex() and EVP_CIPHER_CTX_set_padding() appeared in 590OpenSSL 0.9.7. 591 592IDEA appeared in OpenSSL 0.9.7 but was often disabled due to 593patent concerns; the last patents expired in 2012. 594 595=cut 596