1=pod 2 3=head1 NAME 4 5EVP_CIPHER_CTX_new, 6EVP_CIPHER_CTX_reset, 7EVP_CIPHER_CTX_free, 8EVP_EncryptInit_ex, 9EVP_EncryptUpdate, 10EVP_EncryptFinal_ex, 11EVP_DecryptInit_ex, 12EVP_DecryptUpdate, 13EVP_DecryptFinal_ex, 14EVP_CipherInit_ex, 15EVP_CipherUpdate, 16EVP_CipherFinal_ex, 17EVP_CIPHER_CTX_set_key_length, 18EVP_CIPHER_CTX_ctrl, 19EVP_EncryptInit, 20EVP_EncryptFinal, 21EVP_DecryptInit, 22EVP_DecryptFinal, 23EVP_CipherInit, 24EVP_CipherFinal, 25EVP_get_cipherbyname, 26EVP_get_cipherbynid, 27EVP_get_cipherbyobj, 28EVP_CIPHER_nid, 29EVP_CIPHER_block_size, 30EVP_CIPHER_key_length, 31EVP_CIPHER_iv_length, 32EVP_CIPHER_flags, 33EVP_CIPHER_mode, 34EVP_CIPHER_type, 35EVP_CIPHER_CTX_cipher, 36EVP_CIPHER_CTX_nid, 37EVP_CIPHER_CTX_block_size, 38EVP_CIPHER_CTX_key_length, 39EVP_CIPHER_CTX_iv_length, 40EVP_CIPHER_CTX_get_app_data, 41EVP_CIPHER_CTX_set_app_data, 42EVP_CIPHER_CTX_type, 43EVP_CIPHER_CTX_flags, 44EVP_CIPHER_CTX_mode, 45EVP_CIPHER_param_to_asn1, 46EVP_CIPHER_asn1_to_param, 47EVP_CIPHER_CTX_set_padding, 48EVP_enc_null 49- EVP cipher routines 50 51=head1 SYNOPSIS 52 53=for comment generic 54 55 #include <openssl/evp.h> 56 57 EVP_CIPHER_CTX *EVP_CIPHER_CTX_new(void); 58 int EVP_CIPHER_CTX_reset(EVP_CIPHER_CTX *ctx); 59 void EVP_CIPHER_CTX_free(EVP_CIPHER_CTX *ctx); 60 61 int EVP_EncryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 62 ENGINE *impl, const unsigned char *key, const unsigned char *iv); 63 int EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, 64 int *outl, const unsigned char *in, int inl); 65 int EVP_EncryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl); 66 67 int EVP_DecryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 68 ENGINE *impl, const unsigned char *key, const unsigned char *iv); 69 int EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, 70 int *outl, const unsigned char *in, int inl); 71 int EVP_DecryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl); 72 73 int EVP_CipherInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 74 ENGINE *impl, const unsigned char *key, const unsigned char *iv, int enc); 75 int EVP_CipherUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, 76 int *outl, const unsigned char *in, int inl); 77 int EVP_CipherFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl); 78 79 int EVP_EncryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 80 const unsigned char *key, const unsigned char *iv); 81 int EVP_EncryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl); 82 83 int EVP_DecryptInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 84 const unsigned char *key, const unsigned char *iv); 85 int EVP_DecryptFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl); 86 87 int EVP_CipherInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 88 const unsigned char *key, const unsigned char *iv, int enc); 89 int EVP_CipherFinal(EVP_CIPHER_CTX *ctx, unsigned char *outm, int *outl); 90 91 int EVP_CIPHER_CTX_set_padding(EVP_CIPHER_CTX *x, int padding); 92 int EVP_CIPHER_CTX_set_key_length(EVP_CIPHER_CTX *x, int keylen); 93 int EVP_CIPHER_CTX_ctrl(EVP_CIPHER_CTX *ctx, int type, int arg, void *ptr); 94 int EVP_CIPHER_CTX_rand_key(EVP_CIPHER_CTX *ctx, unsigned char *key); 95 96 const EVP_CIPHER *EVP_get_cipherbyname(const char *name); 97 const EVP_CIPHER *EVP_get_cipherbynid(int nid); 98 const EVP_CIPHER *EVP_get_cipherbyobj(const ASN1_OBJECT *a); 99 100 int EVP_CIPHER_nid(const EVP_CIPHER *e); 101 int EVP_CIPHER_block_size(const EVP_CIPHER *e); 102 int EVP_CIPHER_key_length(const EVP_CIPHER *e); 103 int EVP_CIPHER_iv_length(const EVP_CIPHER *e); 104 unsigned long EVP_CIPHER_flags(const EVP_CIPHER *e); 105 unsigned long EVP_CIPHER_mode(const EVP_CIPHER *e); 106 int EVP_CIPHER_type(const EVP_CIPHER *ctx); 107 108 const EVP_CIPHER *EVP_CIPHER_CTX_cipher(const EVP_CIPHER_CTX *ctx); 109 int EVP_CIPHER_CTX_nid(const EVP_CIPHER_CTX *ctx); 110 int EVP_CIPHER_CTX_block_size(const EVP_CIPHER_CTX *ctx); 111 int EVP_CIPHER_CTX_key_length(const EVP_CIPHER_CTX *ctx); 112 int EVP_CIPHER_CTX_iv_length(const EVP_CIPHER_CTX *ctx); 113 void *EVP_CIPHER_CTX_get_app_data(const EVP_CIPHER_CTX *ctx); 114 void EVP_CIPHER_CTX_set_app_data(const EVP_CIPHER_CTX *ctx, void *data); 115 int EVP_CIPHER_CTX_type(const EVP_CIPHER_CTX *ctx); 116 int EVP_CIPHER_CTX_mode(const EVP_CIPHER_CTX *ctx); 117 118 int EVP_CIPHER_param_to_asn1(EVP_CIPHER_CTX *c, ASN1_TYPE *type); 119 int EVP_CIPHER_asn1_to_param(EVP_CIPHER_CTX *c, ASN1_TYPE *type); 120 121=head1 DESCRIPTION 122 123The EVP cipher routines are a high-level interface to certain 124symmetric ciphers. 125 126EVP_CIPHER_CTX_new() creates a cipher context. 127 128EVP_CIPHER_CTX_free() clears all information from a cipher context 129and free up any allocated memory associate with it, including B<ctx> 130itself. This function should be called after all operations using a 131cipher are complete so sensitive information does not remain in 132memory. 133 134EVP_EncryptInit_ex() sets up cipher context B<ctx> for encryption 135with cipher B<type> from ENGINE B<impl>. B<ctx> must be created 136before calling this function. B<type> is normally supplied 137by a function such as EVP_aes_256_cbc(). If B<impl> is NULL then the 138default implementation is used. B<key> is the symmetric key to use 139and B<iv> is the IV to use (if necessary), the actual number of bytes 140used for the key and IV depends on the cipher. It is possible to set 141all parameters to NULL except B<type> in an initial call and supply 142the remaining parameters in subsequent calls, all of which have B<type> 143set to NULL. This is done when the default cipher parameters are not 144appropriate. 145 146EVP_EncryptUpdate() encrypts B<inl> bytes from the buffer B<in> and 147writes the encrypted version to B<out>. This function can be called 148multiple times to encrypt successive blocks of data. The amount 149of data written depends on the block alignment of the encrypted data. 150For most ciphers and modes, the amount of data written can be anything 151from zero bytes to (inl + cipher_block_size - 1) bytes. 152For wrap cipher modes, the amount of data written can be anything 153from zero bytes to (inl + cipher_block_size) bytes. 154For stream ciphers, the amount of data written can be anything from zero 155bytes to inl bytes. 156Thus, B<out> should contain sufficient room for the operation being performed. 157The actual number of bytes written is placed in B<outl>. It also 158checks if B<in> and B<out> are partially overlapping, and if they are 1590 is returned to indicate failure. 160 161If padding is enabled (the default) then EVP_EncryptFinal_ex() encrypts 162the "final" data, that is any data that remains in a partial block. 163It uses standard block padding (aka PKCS padding) as described in 164the NOTES section, below. The encrypted 165final data is written to B<out> which should have sufficient space for 166one cipher block. The number of bytes written is placed in B<outl>. After 167this function is called the encryption operation is finished and no further 168calls to EVP_EncryptUpdate() should be made. 169 170If padding is disabled then EVP_EncryptFinal_ex() will not encrypt any more 171data and it will return an error if any data remains in a partial block: 172that is if the total data length is not a multiple of the block size. 173 174EVP_DecryptInit_ex(), EVP_DecryptUpdate() and EVP_DecryptFinal_ex() are the 175corresponding decryption operations. EVP_DecryptFinal() will return an 176error code if padding is enabled and the final block is not correctly 177formatted. The parameters and restrictions are identical to the encryption 178operations except that if padding is enabled the decrypted data buffer B<out> 179passed to EVP_DecryptUpdate() should have sufficient room for 180(B<inl> + cipher_block_size) bytes unless the cipher block size is 1 in 181which case B<inl> bytes is sufficient. 182 183EVP_CipherInit_ex(), EVP_CipherUpdate() and EVP_CipherFinal_ex() are 184functions that can be used for decryption or encryption. The operation 185performed depends on the value of the B<enc> parameter. It should be set 186to 1 for encryption, 0 for decryption and -1 to leave the value unchanged 187(the actual value of 'enc' being supplied in a previous call). 188 189EVP_CIPHER_CTX_reset() clears all information from a cipher context 190and free up any allocated memory associate with it, except the B<ctx> 191itself. This function should be called anytime B<ctx> is to be reused 192for another EVP_CipherInit() / EVP_CipherUpdate() / EVP_CipherFinal() 193series of calls. 194 195EVP_EncryptInit(), EVP_DecryptInit() and EVP_CipherInit() behave in a 196similar way to EVP_EncryptInit_ex(), EVP_DecryptInit_ex() and 197EVP_CipherInit_ex() except they always use the default cipher implementation. 198 199EVP_EncryptFinal(), EVP_DecryptFinal() and EVP_CipherFinal() are 200identical to EVP_EncryptFinal_ex(), EVP_DecryptFinal_ex() and 201EVP_CipherFinal_ex(). In previous releases they also cleaned up 202the B<ctx>, but this is no longer done and EVP_CIPHER_CTX_clean() 203must be called to free any context resources. 204 205EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj() 206return an EVP_CIPHER structure when passed a cipher name, a NID or an 207ASN1_OBJECT structure. 208 209EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return the NID of a cipher when 210passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> structure. The actual NID 211value is an internal value which may not have a corresponding OBJECT 212IDENTIFIER. 213 214EVP_CIPHER_CTX_set_padding() enables or disables padding. This 215function should be called after the context is set up for encryption 216or decryption with EVP_EncryptInit_ex(), EVP_DecryptInit_ex() or 217EVP_CipherInit_ex(). By default encryption operations are padded using 218standard block padding and the padding is checked and removed when 219decrypting. If the B<pad> parameter is zero then no padding is 220performed, the total amount of data encrypted or decrypted must then 221be a multiple of the block size or an error will occur. 222 223EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key 224length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> 225structure. The constant B<EVP_MAX_KEY_LENGTH> is the maximum key length 226for all ciphers. Note: although EVP_CIPHER_key_length() is fixed for a 227given cipher, the value of EVP_CIPHER_CTX_key_length() may be different 228for variable key length ciphers. 229 230EVP_CIPHER_CTX_set_key_length() sets the key length of the cipher ctx. 231If the cipher is a fixed length cipher then attempting to set the key 232length to any value other than the fixed value is an error. 233 234EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV 235length of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX>. 236It will return zero if the cipher does not use an IV. The constant 237B<EVP_MAX_IV_LENGTH> is the maximum IV length for all ciphers. 238 239EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block 240size of a cipher when passed an B<EVP_CIPHER> or B<EVP_CIPHER_CTX> 241structure. The constant B<EVP_MAX_BLOCK_LENGTH> is also the maximum block 242length for all ciphers. 243 244EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the type of the passed 245cipher or context. This "type" is the actual NID of the cipher OBJECT 246IDENTIFIER as such it ignores the cipher parameters and 40 bit RC2 and 247128 bit RC2 have the same NID. If the cipher does not have an object 248identifier or does not have ASN1 support this function will return 249B<NID_undef>. 250 251EVP_CIPHER_CTX_cipher() returns the B<EVP_CIPHER> structure when passed 252an B<EVP_CIPHER_CTX> structure. 253 254EVP_CIPHER_mode() and EVP_CIPHER_CTX_mode() return the block cipher mode: 255EVP_CIPH_ECB_MODE, EVP_CIPH_CBC_MODE, EVP_CIPH_CFB_MODE, EVP_CIPH_OFB_MODE, 256EVP_CIPH_CTR_MODE, EVP_CIPH_GCM_MODE, EVP_CIPH_CCM_MODE, EVP_CIPH_XTS_MODE, 257EVP_CIPH_WRAP_MODE or EVP_CIPH_OCB_MODE. If the cipher is a stream cipher then 258EVP_CIPH_STREAM_CIPHER is returned. 259 260EVP_CIPHER_param_to_asn1() sets the AlgorithmIdentifier "parameter" based 261on the passed cipher. This will typically include any parameters and an 262IV. The cipher IV (if any) must be set when this call is made. This call 263should be made before the cipher is actually "used" (before any 264EVP_EncryptUpdate(), EVP_DecryptUpdate() calls for example). This function 265may fail if the cipher does not have any ASN1 support. 266 267EVP_CIPHER_asn1_to_param() sets the cipher parameters based on an ASN1 268AlgorithmIdentifier "parameter". The precise effect depends on the cipher 269In the case of RC2, for example, it will set the IV and effective key length. 270This function should be called after the base cipher type is set but before 271the key is set. For example EVP_CipherInit() will be called with the IV and 272key set to NULL, EVP_CIPHER_asn1_to_param() will be called and finally 273EVP_CipherInit() again with all parameters except the key set to NULL. It is 274possible for this function to fail if the cipher does not have any ASN1 support 275or the parameters cannot be set (for example the RC2 effective key length 276is not supported. 277 278EVP_CIPHER_CTX_ctrl() allows various cipher specific parameters to be determined 279and set. 280 281EVP_CIPHER_CTX_rand_key() generates a random key of the appropriate length 282based on the cipher context. The EVP_CIPHER can provide its own random key 283generation routine to support keys of a specific form. B<Key> must point to a 284buffer at least as big as the value returned by EVP_CIPHER_CTX_key_length(). 285 286=head1 RETURN VALUES 287 288EVP_CIPHER_CTX_new() returns a pointer to a newly created 289B<EVP_CIPHER_CTX> for success and B<NULL> for failure. 290 291EVP_EncryptInit_ex(), EVP_EncryptUpdate() and EVP_EncryptFinal_ex() 292return 1 for success and 0 for failure. 293 294EVP_DecryptInit_ex() and EVP_DecryptUpdate() return 1 for success and 0 for failure. 295EVP_DecryptFinal_ex() returns 0 if the decrypt failed or 1 for success. 296 297EVP_CipherInit_ex() and EVP_CipherUpdate() return 1 for success and 0 for failure. 298EVP_CipherFinal_ex() returns 0 for a decryption failure or 1 for success. 299 300EVP_CIPHER_CTX_reset() returns 1 for success and 0 for failure. 301 302EVP_get_cipherbyname(), EVP_get_cipherbynid() and EVP_get_cipherbyobj() 303return an B<EVP_CIPHER> structure or NULL on error. 304 305EVP_CIPHER_nid() and EVP_CIPHER_CTX_nid() return a NID. 306 307EVP_CIPHER_block_size() and EVP_CIPHER_CTX_block_size() return the block 308size. 309 310EVP_CIPHER_key_length() and EVP_CIPHER_CTX_key_length() return the key 311length. 312 313EVP_CIPHER_CTX_set_padding() always returns 1. 314 315EVP_CIPHER_iv_length() and EVP_CIPHER_CTX_iv_length() return the IV 316length or zero if the cipher does not use an IV. 317 318EVP_CIPHER_type() and EVP_CIPHER_CTX_type() return the NID of the cipher's 319OBJECT IDENTIFIER or NID_undef if it has no defined OBJECT IDENTIFIER. 320 321EVP_CIPHER_CTX_cipher() returns an B<EVP_CIPHER> structure. 322 323EVP_CIPHER_param_to_asn1() and EVP_CIPHER_asn1_to_param() return greater 324than zero for success and zero or a negative number on failure. 325 326EVP_CIPHER_CTX_rand_key() returns 1 for success. 327 328=head1 CIPHER LISTING 329 330All algorithms have a fixed key length unless otherwise stated. 331 332Refer to L<SEE ALSO> for the full list of ciphers available through the EVP 333interface. 334 335=over 4 336 337=item EVP_enc_null() 338 339Null cipher: does nothing. 340 341=back 342 343=head1 AEAD Interface 344 345The EVP interface for Authenticated Encryption with Associated Data (AEAD) 346modes are subtly altered and several additional I<ctrl> operations are supported 347depending on the mode specified. 348 349To specify additional authenticated data (AAD), a call to EVP_CipherUpdate(), 350EVP_EncryptUpdate() or EVP_DecryptUpdate() should be made with the output 351parameter B<out> set to B<NULL>. 352 353When decrypting, the return value of EVP_DecryptFinal() or EVP_CipherFinal() 354indicates whether the operation was successful. If it does not indicate success, 355the authentication operation has failed and any output data B<MUST NOT> be used 356as it is corrupted. 357 358=head2 GCM and OCB Modes 359 360The following I<ctrl>s are supported in GCM and OCB modes. 361 362=over 4 363 364=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_IVLEN, ivlen, NULL) 365 366Sets the IV length. This call can only be made before specifying an IV. If 367not called a default IV length is used. 368 369For GCM AES and OCB AES the default is 12 (i.e. 96 bits). For OCB mode the 370maximum is 15. 371 372=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, taglen, tag) 373 374Writes C<taglen> bytes of the tag value to the buffer indicated by C<tag>. 375This call can only be made when encrypting data and B<after> all data has been 376processed (e.g. after an EVP_EncryptFinal() call). 377 378For OCB, C<taglen> must either be 16 or the value previously set via 379B<EVP_CTRL_AEAD_SET_TAG>. 380 381=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, taglen, tag) 382 383When decrypting, this call sets the expected tag to C<taglen> bytes from C<tag>. 384C<taglen> must be between 1 and 16 inclusive. 385The tag must be set prior to any call to EVP_DecryptFinal() or 386EVP_DecryptFinal_ex(). 387 388For GCM, this call is only valid when decrypting data. 389 390For OCB, this call is valid when decrypting data to set the expected tag, 391and when encrypting to set the desired tag length. 392 393In OCB mode, calling this when encrypting with C<tag> set to C<NULL> sets the 394tag length. The tag length can only be set before specifying an IV. If this is 395not called prior to setting the IV during encryption, then a default tag length 396is used. 397 398For OCB AES, the default tag length is 16 (i.e. 128 bits). It is also the 399maximum tag length for OCB. 400 401=back 402 403=head2 CCM Mode 404 405The EVP interface for CCM mode is similar to that of the GCM mode but with a 406few additional requirements and different I<ctrl> values. 407 408For CCM mode, the total plaintext or ciphertext length B<MUST> be passed to 409EVP_CipherUpdate(), EVP_EncryptUpdate() or EVP_DecryptUpdate() with the output 410and input parameters (B<in> and B<out>) set to B<NULL> and the length passed in 411the B<inl> parameter. 412 413The following I<ctrl>s are supported in CCM mode. 414 415=over 4 416 417=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, taglen, tag) 418 419This call is made to set the expected B<CCM> tag value when decrypting or 420the length of the tag (with the C<tag> parameter set to NULL) when encrypting. 421The tag length is often referred to as B<M>. If not set a default value is 422used (12 for AES). When decrypting, the tag needs to be set before passing 423in data to be decrypted, but as in GCM and OCB mode, it can be set after 424passing additional authenticated data (see L<AEAD Interface>). 425 426=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_L, ivlen, NULL) 427 428Sets the CCM B<L> value. If not set a default is used (8 for AES). 429 430=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_IVLEN, ivlen, NULL) 431 432Sets the CCM nonce (IV) length. This call can only be made before specifying 433a nonce value. The nonce length is given by B<15 - L> so it is 7 by default for 434AES. 435 436=back 437 438=head2 ChaCha20-Poly1305 439 440The following I<ctrl>s are supported for the ChaCha20-Poly1305 AEAD algorithm. 441 442=over 4 443 444=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_IVLEN, ivlen, NULL) 445 446Sets the nonce length. This call can only be made before specifying the nonce. 447If not called a default nonce length of 12 (i.e. 96 bits) is used. The maximum 448nonce length is 12 bytes (i.e. 96-bits). If a nonce of less than 12 bytes is set 449then the nonce is automatically padded with leading 0 bytes to make it 12 bytes 450in length. 451 452=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_GET_TAG, taglen, tag) 453 454Writes C<taglen> bytes of the tag value to the buffer indicated by C<tag>. 455This call can only be made when encrypting data and B<after> all data has been 456processed (e.g. after an EVP_EncryptFinal() call). 457 458C<taglen> specified here must be 16 (B<POLY1305_BLOCK_SIZE>, i.e. 128-bits) or 459less. 460 461=item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG, taglen, tag) 462 463Sets the expected tag to C<taglen> bytes from C<tag>. 464The tag length can only be set before specifying an IV. 465C<taglen> must be between 1 and 16 (B<POLY1305_BLOCK_SIZE>) inclusive. 466This call is only valid when decrypting data. 467 468=back 469 470=head1 NOTES 471 472Where possible the B<EVP> interface to symmetric ciphers should be used in 473preference to the low-level interfaces. This is because the code then becomes 474transparent to the cipher used and much more flexible. Additionally, the 475B<EVP> interface will ensure the use of platform specific cryptographic 476acceleration such as AES-NI (the low-level interfaces do not provide the 477guarantee). 478 479PKCS padding works by adding B<n> padding bytes of value B<n> to make the total 480length of the encrypted data a multiple of the block size. Padding is always 481added so if the data is already a multiple of the block size B<n> will equal 482the block size. For example if the block size is 8 and 11 bytes are to be 483encrypted then 5 padding bytes of value 5 will be added. 484 485When decrypting the final block is checked to see if it has the correct form. 486 487Although the decryption operation can produce an error if padding is enabled, 488it is not a strong test that the input data or key is correct. A random block 489has better than 1 in 256 chance of being of the correct format and problems with 490the input data earlier on will not produce a final decrypt error. 491 492If padding is disabled then the decryption operation will always succeed if 493the total amount of data decrypted is a multiple of the block size. 494 495The functions EVP_EncryptInit(), EVP_EncryptFinal(), EVP_DecryptInit(), 496EVP_CipherInit() and EVP_CipherFinal() are obsolete but are retained for 497compatibility with existing code. New code should use EVP_EncryptInit_ex(), 498EVP_EncryptFinal_ex(), EVP_DecryptInit_ex(), EVP_DecryptFinal_ex(), 499EVP_CipherInit_ex() and EVP_CipherFinal_ex() because they can reuse an 500existing context without allocating and freeing it up on each call. 501 502There are some differences between functions EVP_CipherInit() and 503EVP_CipherInit_ex(), significant in some circumstances. EVP_CipherInit() fills 504the passed context object with zeros. As a consequence, EVP_CipherInit() does 505not allow step-by-step initialization of the ctx when the I<key> and I<iv> are 506passed in separate calls. It also means that the flags set for the CTX are 507removed, and it is especially important for the 508B<EVP_CIPHER_CTX_FLAG_WRAP_ALLOW> flag treated specially in 509EVP_CipherInit_ex(). 510 511EVP_get_cipherbynid(), and EVP_get_cipherbyobj() are implemented as macros. 512 513=head1 BUGS 514 515B<EVP_MAX_KEY_LENGTH> and B<EVP_MAX_IV_LENGTH> only refer to the internal 516ciphers with default key lengths. If custom ciphers exceed these values the 517results are unpredictable. This is because it has become standard practice to 518define a generic key as a fixed unsigned char array containing 519B<EVP_MAX_KEY_LENGTH> bytes. 520 521The ASN1 code is incomplete (and sometimes inaccurate) it has only been tested 522for certain common S/MIME ciphers (RC2, DES, triple DES) in CBC mode. 523 524=head1 EXAMPLES 525 526Encrypt a string using IDEA: 527 528 int do_crypt(char *outfile) 529 { 530 unsigned char outbuf[1024]; 531 int outlen, tmplen; 532 /* 533 * Bogus key and IV: we'd normally set these from 534 * another source. 535 */ 536 unsigned char key[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}; 537 unsigned char iv[] = {1,2,3,4,5,6,7,8}; 538 char intext[] = "Some Crypto Text"; 539 EVP_CIPHER_CTX *ctx; 540 FILE *out; 541 542 ctx = EVP_CIPHER_CTX_new(); 543 EVP_EncryptInit_ex(ctx, EVP_idea_cbc(), NULL, key, iv); 544 545 if (!EVP_EncryptUpdate(ctx, outbuf, &outlen, intext, strlen(intext))) { 546 /* Error */ 547 EVP_CIPHER_CTX_free(ctx); 548 return 0; 549 } 550 /* 551 * Buffer passed to EVP_EncryptFinal() must be after data just 552 * encrypted to avoid overwriting it. 553 */ 554 if (!EVP_EncryptFinal_ex(ctx, outbuf + outlen, &tmplen)) { 555 /* Error */ 556 EVP_CIPHER_CTX_free(ctx); 557 return 0; 558 } 559 outlen += tmplen; 560 EVP_CIPHER_CTX_free(ctx); 561 /* 562 * Need binary mode for fopen because encrypted data is 563 * binary data. Also cannot use strlen() on it because 564 * it won't be NUL terminated and may contain embedded 565 * NULs. 566 */ 567 out = fopen(outfile, "wb"); 568 if (out == NULL) { 569 /* Error */ 570 return 0; 571 } 572 fwrite(outbuf, 1, outlen, out); 573 fclose(out); 574 return 1; 575 } 576 577The ciphertext from the above example can be decrypted using the B<openssl> 578utility with the command line (shown on two lines for clarity): 579 580 openssl idea -d \ 581 -K 000102030405060708090A0B0C0D0E0F -iv 0102030405060708 <filename 582 583General encryption and decryption function example using FILE I/O and AES128 584with a 128-bit key: 585 586 int do_crypt(FILE *in, FILE *out, int do_encrypt) 587 { 588 /* Allow enough space in output buffer for additional block */ 589 unsigned char inbuf[1024], outbuf[1024 + EVP_MAX_BLOCK_LENGTH]; 590 int inlen, outlen; 591 EVP_CIPHER_CTX *ctx; 592 /* 593 * Bogus key and IV: we'd normally set these from 594 * another source. 595 */ 596 unsigned char key[] = "0123456789abcdeF"; 597 unsigned char iv[] = "1234567887654321"; 598 599 /* Don't set key or IV right away; we want to check lengths */ 600 ctx = EVP_CIPHER_CTX_new(); 601 EVP_CipherInit_ex(ctx, EVP_aes_128_cbc(), NULL, NULL, NULL, 602 do_encrypt); 603 OPENSSL_assert(EVP_CIPHER_CTX_key_length(ctx) == 16); 604 OPENSSL_assert(EVP_CIPHER_CTX_iv_length(ctx) == 16); 605 606 /* Now we can set key and IV */ 607 EVP_CipherInit_ex(ctx, NULL, NULL, key, iv, do_encrypt); 608 609 for (;;) { 610 inlen = fread(inbuf, 1, 1024, in); 611 if (inlen <= 0) 612 break; 613 if (!EVP_CipherUpdate(ctx, outbuf, &outlen, inbuf, inlen)) { 614 /* Error */ 615 EVP_CIPHER_CTX_free(ctx); 616 return 0; 617 } 618 fwrite(outbuf, 1, outlen, out); 619 } 620 if (!EVP_CipherFinal_ex(ctx, outbuf, &outlen)) { 621 /* Error */ 622 EVP_CIPHER_CTX_free(ctx); 623 return 0; 624 } 625 fwrite(outbuf, 1, outlen, out); 626 627 EVP_CIPHER_CTX_free(ctx); 628 return 1; 629 } 630 631 632=head1 SEE ALSO 633 634L<evp(7)> 635 636Supported ciphers are listed in: 637 638L<EVP_aes(3)>, 639L<EVP_aria(3)>, 640L<EVP_bf(3)>, 641L<EVP_camellia(3)>, 642L<EVP_cast5(3)>, 643L<EVP_chacha20(3)>, 644L<EVP_des(3)>, 645L<EVP_desx(3)>, 646L<EVP_idea(3)>, 647L<EVP_rc2(3)>, 648L<EVP_rc4(3)>, 649L<EVP_rc5(3)>, 650L<EVP_seed(3)>, 651L<EVP_sm4(3)> 652 653=head1 HISTORY 654 655Support for OCB mode was added in OpenSSL 1.1.0. 656 657B<EVP_CIPHER_CTX> was made opaque in OpenSSL 1.1.0. As a result, 658EVP_CIPHER_CTX_reset() appeared and EVP_CIPHER_CTX_cleanup() 659disappeared. EVP_CIPHER_CTX_init() remains as an alias for 660EVP_CIPHER_CTX_reset(). 661 662=head1 COPYRIGHT 663 664Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved. 665 666Licensed under the OpenSSL license (the "License"). You may not use 667this file except in compliance with the License. You can obtain a copy 668in the file LICENSE in the source distribution or at 669L<https://www.openssl.org/source/license.html>. 670 671=cut 672