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_idea_cbc, 23EVP_idea_ecb, EVP_idea_cfb, EVP_idea_ofb, EVP_idea_cbc, 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 - EVP cipher routines 30 31=head1 SYNOPSIS 32 33 #include <openssl/evp.h> 34 35 void EVP_CIPHER_CTX_init(EVP_CIPHER_CTX *a); 36 37 int EVP_EncryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 38 ENGINE *impl, unsigned char *key, unsigned char *iv); 39 int EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, 40 int *outl, unsigned char *in, int inl); 41 int EVP_EncryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *out, 42 int *outl); 43 44 int EVP_DecryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 45 ENGINE *impl, unsigned char *key, unsigned char *iv); 46 int EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, 47 int *outl, unsigned char *in, int inl); 48 int EVP_DecryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm, 49 int *outl); 50 51 int EVP_CipherInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 52 ENGINE *impl, unsigned char *key, unsigned char *iv, int enc); 53 int EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, 54 int *outl, unsigned char *in, int inl); 55 int EVP_CipherFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm, 56 int *outl); 57 58 int EVP_EncryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 59 unsigned char *key, unsigned char *iv); 60 int EVP_EncryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, 61 int *outl); 62 63 int EVP_DecryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 64 unsigned char *key, unsigned char *iv); 65 int EVP_DecryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, 66 int *outl); 67 68 int EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 69 unsigned char *key, unsigned char *iv, int enc); 70 int EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, 71 int *outl); 72 73 int EVP_CIPHER_CTX_set_padding(EVP_CIPHER_CTX *x, int padding); 74 int EVP_CIPHER_CTX_set_key_length(EVP_CIPHER_CTX *x, int keylen); 75 int EVP_CIPHER_CTX_ctrl(EVP_CIPHER_CTX *ctx, int type, int arg, void *ptr); 76 int EVP_CIPHER_CTX_cleanup(EVP_CIPHER_CTX *a); 77 78 const EVP_CIPHER *EVP_get_cipherbyname(const char *name); 79 #define EVP_get_cipherbynid(a) EVP_get_cipherbyname(OBJ_nid2sn(a)) 80 #define EVP_get_cipherbyobj(a) EVP_get_cipherbynid(OBJ_obj2nid(a)) 81 82 #define EVP_CIPHER_nid(e) ((e)->nid) 83 #define EVP_CIPHER_block_size(e) ((e)->block_size) 84 #define EVP_CIPHER_key_length(e) ((e)->key_len) 85 #define EVP_CIPHER_iv_length(e) ((e)->iv_len) 86 #define EVP_CIPHER_flags(e) ((e)->flags) 87 #define EVP_CIPHER_mode(e) ((e)->flags) & EVP_CIPH_MODE) 88 int EVP_CIPHER_type(const EVP_CIPHER *ctx); 89 90 #define EVP_CIPHER_CTX_cipher(e) ((e)->cipher) 91 #define EVP_CIPHER_CTX_nid(e) ((e)->cipher->nid) 92 #define EVP_CIPHER_CTX_block_size(e) ((e)->cipher->block_size) 93 #define EVP_CIPHER_CTX_key_length(e) ((e)->key_len) 94 #define EVP_CIPHER_CTX_iv_length(e) ((e)->cipher->iv_len) 95 #define EVP_CIPHER_CTX_get_app_data(e) ((e)->app_data) 96 #define EVP_CIPHER_CTX_set_app_data(e,d) ((e)->app_data=(char *)(d)) 97 #define EVP_CIPHER_CTX_type(c) EVP_CIPHER_type(EVP_CIPHER_CTX_cipher(c)) 98 #define EVP_CIPHER_CTX_flags(e) ((e)->cipher->flags) 99 #define EVP_CIPHER_CTX_mode(e) ((e)->cipher->flags & EVP_CIPH_MODE) 100 101 int EVP_CIPHER_param_to_asn1(EVP_CIPHER_CTX *c, ASN1_TYPE *type); 102 int EVP_CIPHER_asn1_to_param(EVP_CIPHER_CTX *c, ASN1_TYPE *type); 103 104=head1 DESCRIPTION 105 106The EVP cipher routines are a high level interface to certain 107symmetric ciphers. 108 109EVP_CIPHER_CTX_init() initializes cipher contex B<ctx>. 110 111EVP_EncryptInit_ex() sets up cipher context B<ctx> for encryption 112with cipher B<type> from ENGINE B<impl>. B<ctx> must be initialized 113before calling this function. B<type> is normally supplied 114by a function such as EVP_des_cbc(). If B<impl> is NULL then the 115default implementation is used. B<key> is the symmetric key to use 116and B<iv> is the IV to use (if necessary), the actual number of bytes 117used for the key and IV depends on the cipher. It is possible to set 118all parameters to NULL except B<type> in an initial call and supply 119the remaining parameters in subsequent calls, all of which have B<type> 120set to NULL. This is done when the default cipher parameters are not 121appropriate. 122 123EVP_EncryptUpdate() encrypts B<inl> bytes from the buffer B<in> and 124writes the encrypted version to B<out>. This function can be called 125multiple times to encrypt successive blocks of data. The amount 126of data written depends on the block alignment of the encrypted data: 127as a result the amount of data written may be anything from zero bytes 128to (inl + cipher_block_size - 1) so B<out> should contain sufficient 129room. The actual number of bytes written is placed in B<outl>. 130 131If padding is enabled (the default) then EVP_EncryptFinal_ex() encrypts 132the "final" data, that is any data that remains in a partial block. 133It uses L<standard block padding|/NOTES> (aka PKCS padding). The encrypted 134final data is written to B<out> which should have sufficient space for 135one cipher block. The number of bytes written is placed in B<outl>. After 136this function is called the encryption operation is finished and no further 137calls to EVP_EncryptUpdate() should be made. 138 139If padding is disabled then EVP_EncryptFinal_ex() will not encrypt any more 140data and it will return an error if any data remains in a partial block: 141that is if the total data length is not a multiple of the block size. 142 143EVP_DecryptInit_ex(), EVP_DecryptUpdate() and EVP_DecryptFinal_ex() are the 144corresponding decryption operations. EVP_DecryptFinal() will return an 145error code if padding is enabled and the final block is not correctly 146formatted. The parameters and restrictions are identical to the encryption 147operations except that if padding is enabled the decrypted data buffer B<out> 148passed to EVP_DecryptUpdate() should have sufficient room for 149(B<inl> + cipher_block_size) bytes unless the cipher block size is 1 in 150which case B<inl> bytes is sufficient. 151 152EVP_CipherInit_ex(), EVP_CipherUpdate() and EVP_CipherFinal_ex() are 153functions that can be used for decryption or encryption. The operation 154performed depends on the value of the B<enc> parameter. It should be set 155to 1 for encryption, 0 for decryption and -1 to leave the value unchanged 156(the actual value of 'enc' being supplied in a previous call). 157 158EVP_CIPHER_CTX_cleanup() clears all information from a cipher context 159and free up any allocated memory associate with it. It should be called 160after all operations using a cipher are complete so sensitive information 161does not remain in memory. 162 163EVP_EncryptInit(), EVP_DecryptInit() and EVP_CipherInit() behave in a 164similar way to EVP_EncryptInit_ex(), EVP_DecryptInit_ex and 165EVP_CipherInit_ex() except the B<ctx> parameter does not need to be 166initialized and they always use the default cipher implementation. 167 168EVP_EncryptFinal(), EVP_DecryptFinal() and EVP_CipherFinal() behave in a 169similar way to EVP_EncryptFinal_ex(), EVP_DecryptFinal_ex() and 170EVP_CipherFinal_ex() except B<ctx> is automatically cleaned up 171after the call. 172 173EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj() 174return an EVP_CIPHER structure when passed a cipher name, a NID or an 175ASN1_OBJECT structure. 176 177EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return the NID of a cipher when 178passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> structure. The actual NID 179value is an internal value which may not have a corresponding OBJECT 180IDENTIFIER. 181 182EVP_CIPHER_CTX_set_padding() enables or disables padding. By default 183encryption operations are padded using standard block padding and the 184padding is checked and removed when decrypting. If the B<pad> parameter 185is zero then no padding is performed, the total amount of data encrypted 186or decrypted must then be a multiple of the block size or an error will 187occur. 188 189EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key 190length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> 191structure. The constant B<EVP_MAX_KEY_LENGTH> is the maximum key length 192for all ciphers. Note: although EVP_CIPHER_key_length() is fixed for a 193given cipher, the value of EVP_CIPHER_CTX_key_length() may be different 194for variable key length ciphers. 195 196EVP_CIPHER_CTX_set_key_length() sets the key length of the cipher ctx. 197If the cipher is a fixed length cipher then attempting to set the key 198length to any value other than the fixed value is an error. 199 200EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV 201length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>. 202It will return zero if the cipher does not use an IV. The constant 203B<EVP_MAX_IV_LENGTH> is the maximum IV length for all ciphers. 204 205EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block 206size of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> 207structure. The constant B<EVP_MAX_IV_LENGTH> is also the maximum block 208length for all ciphers. 209 210EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the type of the passed 211cipher or context. This "type" is the actual NID of the cipher OBJECT 212IDENTIFIER as such it ignores the cipher parameters and 40 bit RC2 and 213128 bit RC2 have the same NID. If the cipher does not have an object 214identifier or does not have ASN1 support this function will return 215B<NID_undef>. 216 217EVP_CIPHER_CTX_cipher() returns the B<EVP_CIPHER> structure when passed 218an B<EVP_CIPHER_CTX> structure. 219 220EVP_CIPHER_mode() and EVP_CIPHER_CTX_mode() return the block cipher mode: 221EVP_CIPH_ECB_MODE, EVP_CIPH_CBC_MODE, EVP_CIPH_CFB_MODE or 222EVP_CIPH_OFB_MODE. If the cipher is a stream cipher then 223EVP_CIPH_STREAM_CIPHER is returned. 224 225EVP_CIPHER_param_to_asn1() sets the AlgorithmIdentifier "parameter" based 226on the passed cipher. This will typically include any parameters and an 227IV. The cipher IV (if any) must be set when this call is made. This call 228should be made before the cipher is actually "used" (before any 229EVP_EncryptUpdate(), EVP_DecryptUpdate() calls for example). This function 230may fail if the cipher does not have any ASN1 support. 231 232EVP_CIPHER_asn1_to_param() sets the cipher parameters based on an ASN1 233AlgorithmIdentifier "parameter". The precise effect depends on the cipher 234In the case of RC2, for example, it will set the IV and effective key length. 235This function should be called after the base cipher type is set but before 236the key is set. For example EVP_CipherInit() will be called with the IV and 237key set to NULL, EVP_CIPHER_asn1_to_param() will be called and finally 238EVP_CipherInit() again with all parameters except the key set to NULL. It is 239possible for this function to fail if the cipher does not have any ASN1 support 240or the parameters cannot be set (for example the RC2 effective key length 241is not supported. 242 243EVP_CIPHER_CTX_ctrl() allows various cipher specific parameters to be determined 244and set. 245 246=head1 RETURN VALUES 247 248EVP_EncryptInit_ex(), EVP_EncryptUpdate() and EVP_EncryptFinal_ex() 249return 1 for success and 0 for failure. 250 251EVP_DecryptInit_ex() and EVP_DecryptUpdate() return 1 for success and 0 for failure. 252EVP_DecryptFinal_ex() returns 0 if the decrypt failed or 1 for success. 253 254EVP_CipherInit_ex() and EVP_CipherUpdate() return 1 for success and 0 for failure. 255EVP_CipherFinal_ex() returns 0 for a decryption failure or 1 for success. 256 257EVP_CIPHER_CTX_cleanup() returns 1 for success and 0 for failure. 258 259EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj() 260return an B<EVP_CIPHER> structure or NULL on error. 261 262EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return a NID. 263 264EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block 265size. 266 267EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key 268length. 269 270EVP_CIPHER_CTX_set_padding() always returns 1. 271 272EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV 273length or zero if the cipher does not use an IV. 274 275EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the NID of the cipher's 276OBJECT IDENTIFIER or NID_undef if it has no defined OBJECT IDENTIFIER. 277 278EVP_CIPHER_CTX_cipher() returns an B<EVP_CIPHER> structure. 279 280EVP_CIPHER_param_to_asn1() and EVP_CIPHER_asn1_to_param() return 1 for 281success or zero for failure. 282 283=head1 CIPHER LISTING 284 285All algorithms have a fixed key length unless otherwise stated. 286 287=over 4 288 289=item EVP_enc_null() 290 291Null cipher: does nothing. 292 293=item EVP_des_cbc(void), EVP_des_ecb(void), EVP_des_cfb(void), EVP_des_ofb(void) 294 295DES in CBC, ECB, CFB and OFB modes respectively. 296 297=item EVP_des_ede_cbc(void), EVP_des_ede(), EVP_des_ede_ofb(void), EVP_des_ede_cfb(void) 298 299Two key triple DES in CBC, ECB, CFB and OFB modes respectively. 300 301=item EVP_des_ede3_cbc(void), EVP_des_ede3(), EVP_des_ede3_ofb(void), EVP_des_ede3_cfb(void) 302 303Three key triple DES in CBC, ECB, CFB and OFB modes respectively. 304 305=item EVP_desx_cbc(void) 306 307DESX algorithm in CBC mode. 308 309=item EVP_rc4(void) 310 311RC4 stream cipher. This is a variable key length cipher with default key length 128 bits. 312 313=item EVP_rc4_40(void) 314 315RC4 stream cipher with 40 bit key length. This is obsolete and new code should use EVP_rc4() 316and the EVP_CIPHER_CTX_set_key_length() function. 317 318=item EVP_idea_cbc() EVP_idea_ecb(void), EVP_idea_cfb(void), EVP_idea_ofb(void), EVP_idea_cbc(void) 319 320IDEA encryption algorithm in CBC, ECB, CFB and OFB modes respectively. 321 322=item EVP_rc2_cbc(void), EVP_rc2_ecb(void), EVP_rc2_cfb(void), EVP_rc2_ofb(void) 323 324RC2 encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key 325length cipher with an additional parameter called "effective key bits" or "effective key length". 326By default both are set to 128 bits. 327 328=item EVP_rc2_40_cbc(void), EVP_rc2_64_cbc(void) 329 330RC2 algorithm in CBC mode with a default key length and effective key length of 40 and 64 bits. 331These are obsolete and new code should use EVP_rc2_cbc(), EVP_CIPHER_CTX_set_key_length() and 332EVP_CIPHER_CTX_ctrl() to set the key length and effective key length. 333 334=item EVP_bf_cbc(void), EVP_bf_ecb(void), EVP_bf_cfb(void), EVP_bf_ofb(void); 335 336Blowfish encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key 337length cipher. 338 339=item EVP_cast5_cbc(void), EVP_cast5_ecb(void), EVP_cast5_cfb(void), EVP_cast5_ofb(void) 340 341CAST encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key 342length cipher. 343 344=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) 345 346RC5 encryption algorithm in CBC, ECB, CFB and OFB modes respectively. This is a variable key length 347cipher with an additional "number of rounds" parameter. By default the key length is set to 128 348bits and 12 rounds. 349 350=item EVP_aes_128_gcm(void), EVP_aes_192_gcm(void), EVP_aes_256_gcm(void) 351 352AES Galois Counter Mode (GCM) for 128, 192 and 256 bit keys respectively. 353These ciphers require additional control operations to function correctly: see 354L<GCM mode> section below for details. 355 356=item EVP_aes_128_ccm(void), EVP_aes_192_ccm(void), EVP_aes_256_ccm(void) 357 358AES Counter with CBC-MAC Mode (CCM) for 128, 192 and 256 bit keys respectively. 359These ciphers require additional control operations to function correctly: see 360CCM mode section below for details. 361 362=back 363 364=head1 GCM Mode 365 366For GCM mode ciphers the behaviour of the EVP interface is subtly altered and 367several GCM specific ctrl operations are supported. 368 369To specify any additional authenticated data (AAD) a call to EVP_CipherUpdate(), 370EVP_EncryptUpdate() or EVP_DecryptUpdate() should be made with the output 371parameter B<out> set to B<NULL>. 372 373When decrypting the return value of EVP_DecryptFinal() or EVP_CipherFinal() 374indicates if the operation was successful. If it does not indicate success 375the authentication operation has failed and any output data B<MUST NOT> 376be used as it is corrupted. 377 378The following ctrls are supported in GCM mode: 379 380 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, ivlen, NULL); 381 382Sets the GCM IV length: this call can only be made before specifying an IV. If 383not called a default IV length is used (96 bits for AES). 384 385 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, taglen, tag); 386 387Writes B<taglen> bytes of the tag value to the buffer indicated by B<tag>. 388This call can only be made when encrypting data and B<after> all data has been 389processed (e.g. after an EVP_EncryptFinal() call). 390 391 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, taglen, tag); 392 393Sets the expected tag to B<taglen> bytes from B<tag>. This call is only legal 394when decrypting data and must be made B<before> any data is processed (e.g. 395before any EVP_DecryptUpdate() call). 396 397See L<EXAMPLES> below for an example of the use of GCM mode. 398 399=head1 CCM Mode 400 401The behaviour of CCM mode ciphers is similar to CCM mode but with a few 402additional requirements and different ctrl values. 403 404Like GCM mode any additional authenticated data (AAD) is passed by calling 405EVP_CipherUpdate(), EVP_EncryptUpdate() or EVP_DecryptUpdate() with the output 406parameter B<out> set to B<NULL>. Additionally the total plaintext or ciphertext 407length B<MUST> be passed to EVP_CipherUpdate(), EVP_EncryptUpdate() or 408EVP_DecryptUpdate() with the output and input parameters (B<in> and B<out>) 409set to B<NULL> and the length passed in the B<inl> parameter. 410 411The following ctrls are supported in CCM mode: 412 413 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_TAG, taglen, tag); 414 415This call is made to set the expected B<CCM> tag value when decrypting or 416the length of the tag (with the B<tag> parameter set to NULL) when encrypting. 417The tag length is often referred to as B<M>. If not set a default value is 418used (12 for AES). 419 420 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_L, ivlen, NULL); 421 422Sets the CCM B<L> value. If not set a default is used (8 for AES). 423 424 EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_IVLEN, ivlen, NULL); 425 426Sets the CCM nonce (IV) length: this call can only be made before specifying 427an nonce value. The nonce length is given by B<15 - L> so it is 7 by default 428for AES. 429 430 431 432=head1 NOTES 433 434Where possible the B<EVP> interface to symmetric ciphers should be used in 435preference to the low level interfaces. This is because the code then becomes 436transparent to the cipher used and much more flexible. Additionally, the 437B<EVP> interface will ensure the use of platform specific cryptographic 438acceleration such as AES-NI (the low level interfaces do not provide the 439guarantee). 440 441PKCS padding works by adding B<n> padding bytes of value B<n> to make the total 442length of the encrypted data a multiple of the block size. Padding is always 443added so if the data is already a multiple of the block size B<n> will equal 444the block size. For example if the block size is 8 and 11 bytes are to be 445encrypted then 5 padding bytes of value 5 will be added. 446 447When decrypting the final block is checked to see if it has the correct form. 448 449Although the decryption operation can produce an error if padding is enabled, 450it is not a strong test that the input data or key is correct. A random block 451has better than 1 in 256 chance of being of the correct format and problems with 452the input data earlier on will not produce a final decrypt error. 453 454If padding is disabled then the decryption operation will always succeed if 455the total amount of data decrypted is a multiple of the block size. 456 457The functions EVP_EncryptInit(), EVP_EncryptFinal(), EVP_DecryptInit(), 458EVP_CipherInit() and EVP_CipherFinal() are obsolete but are retained for 459compatibility with existing code. New code should use EVP_EncryptInit_ex(), 460EVP_EncryptFinal_ex(), EVP_DecryptInit_ex(), EVP_DecryptFinal_ex(), 461EVP_CipherInit_ex() and EVP_CipherFinal_ex() because they can reuse an 462existing context without allocating and freeing it up on each call. 463 464=head1 BUGS 465 466For RC5 the number of rounds can currently only be set to 8, 12 or 16. This is 467a limitation of the current RC5 code rather than the EVP interface. 468 469EVP_MAX_KEY_LENGTH and EVP_MAX_IV_LENGTH only refer to the internal ciphers with 470default key lengths. If custom ciphers exceed these values the results are 471unpredictable. This is because it has become standard practice to define a 472generic key as a fixed unsigned char array containing EVP_MAX_KEY_LENGTH bytes. 473 474The ASN1 code is incomplete (and sometimes inaccurate) it has only been tested 475for certain common S/MIME ciphers (RC2, DES, triple DES) in CBC mode. 476 477=head1 EXAMPLES 478 479Encrypt a string using IDEA: 480 481 int do_crypt(char *outfile) 482 { 483 unsigned char outbuf[1024]; 484 int outlen, tmplen; 485 /* Bogus key and IV: we'd normally set these from 486 * another source. 487 */ 488 unsigned char key[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}; 489 unsigned char iv[] = {1,2,3,4,5,6,7,8}; 490 char intext[] = "Some Crypto Text"; 491 EVP_CIPHER_CTX ctx; 492 FILE *out; 493 494 EVP_CIPHER_CTX_init(&ctx); 495 EVP_EncryptInit_ex(&ctx, EVP_idea_cbc(), NULL, key, iv); 496 497 if(!EVP_EncryptUpdate(&ctx, outbuf, &outlen, intext, strlen(intext))) 498 { 499 /* Error */ 500 return 0; 501 } 502 /* Buffer passed to EVP_EncryptFinal() must be after data just 503 * encrypted to avoid overwriting it. 504 */ 505 if(!EVP_EncryptFinal_ex(&ctx, outbuf + outlen, &tmplen)) 506 { 507 /* Error */ 508 return 0; 509 } 510 outlen += tmplen; 511 EVP_CIPHER_CTX_cleanup(&ctx); 512 /* Need binary mode for fopen because encrypted data is 513 * binary data. Also cannot use strlen() on it because 514 * it wont be null terminated and may contain embedded 515 * nulls. 516 */ 517 out = fopen(outfile, "wb"); 518 fwrite(outbuf, 1, outlen, out); 519 fclose(out); 520 return 1; 521 } 522 523The ciphertext from the above example can be decrypted using the B<openssl> 524utility with the command line (shown on two lines for clarity): 525 526 openssl idea -d <filename 527 -K 000102030405060708090A0B0C0D0E0F -iv 0102030405060708 528 529General encryption and decryption function example using FILE I/O and AES128 530with a 128-bit key: 531 532 int do_crypt(FILE *in, FILE *out, int do_encrypt) 533 { 534 /* Allow enough space in output buffer for additional block */ 535 unsigned char inbuf[1024], outbuf[1024 + EVP_MAX_BLOCK_LENGTH]; 536 int inlen, outlen; 537 EVP_CIPHER_CTX ctx; 538 /* Bogus key and IV: we'd normally set these from 539 * another source. 540 */ 541 unsigned char key[] = "0123456789abcdeF"; 542 unsigned char iv[] = "1234567887654321"; 543 544 /* Don't set key or IV right away; we want to check lengths */ 545 EVP_CIPHER_CTX_init(&ctx); 546 EVP_CipherInit_ex(&ctx, EVP_aes_128_cbc(), NULL, NULL, NULL, 547 do_encrypt); 548 OPENSSL_assert(EVP_CIPHER_CTX_key_length(&ctx) == 16); 549 OPENSSL_assert(EVP_CIPHER_CTX_iv_length(&ctx) == 16); 550 551 /* Now we can set key and IV */ 552 EVP_CipherInit_ex(&ctx, NULL, NULL, key, iv, do_encrypt); 553 554 for(;;) 555 { 556 inlen = fread(inbuf, 1, 1024, in); 557 if(inlen <= 0) break; 558 if(!EVP_CipherUpdate(&ctx, outbuf, &outlen, inbuf, inlen)) 559 { 560 /* Error */ 561 EVP_CIPHER_CTX_cleanup(&ctx); 562 return 0; 563 } 564 fwrite(outbuf, 1, outlen, out); 565 } 566 if(!EVP_CipherFinal_ex(&ctx, outbuf, &outlen)) 567 { 568 /* Error */ 569 EVP_CIPHER_CTX_cleanup(&ctx); 570 return 0; 571 } 572 fwrite(outbuf, 1, outlen, out); 573 574 EVP_CIPHER_CTX_cleanup(&ctx); 575 return 1; 576 } 577 578 579=head1 SEE ALSO 580 581L<evp(3)|evp(3)> 582 583=head1 HISTORY 584 585EVP_CIPHER_CTX_init(), EVP_EncryptInit_ex(), EVP_EncryptFinal_ex(), 586EVP_DecryptInit_ex(), EVP_DecryptFinal_ex(), EVP_CipherInit_ex(), 587EVP_CipherFinal_ex() and EVP_CIPHER_CTX_set_padding() appeared in 588OpenSSL 0.9.7. 589 590IDEA appeared in OpenSSL 0.9.7 but was often disabled due to 591patent concerns; the last patents expired in 2012. 592 593=cut 594