1 /* Copyright (c) 2014, Google Inc. 2 * 3 * Permission to use, copy, modify, and/or distribute this software for any 4 * purpose with or without fee is hereby granted, provided that the above 5 * copyright notice and this permission notice appear in all copies. 6 * 7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY 10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION 12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN 13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */ 14 15 #ifndef OPENSSL_HEADER_AEAD_H 16 #define OPENSSL_HEADER_AEAD_H 17 18 #include <openssl/base.h> 19 20 #if defined(__cplusplus) 21 extern "C" { 22 #endif 23 24 25 /* Authenticated Encryption with Additional Data. 26 * 27 * AEAD couples confidentiality and integrity in a single primtive. AEAD 28 * algorithms take a key and then can seal and open individual messages. Each 29 * message has a unique, per-message nonce and, optionally, additional data 30 * which is authenticated but not included in the ciphertext. 31 * 32 * The |EVP_AEAD_CTX_init| function initialises an |EVP_AEAD_CTX| structure and 33 * performs any precomputation needed to use |aead| with |key|. The length of 34 * the key, |key_len|, is given in bytes. 35 * 36 * The |tag_len| argument contains the length of the tags, in bytes, and allows 37 * for the processing of truncated authenticators. A zero value indicates that 38 * the default tag length should be used and this is defined as 39 * |EVP_AEAD_DEFAULT_TAG_LENGTH| in order to make the code clear. Using 40 * truncated tags increases an attacker's chance of creating a valid forgery. 41 * Be aware that the attacker's chance may increase more than exponentially as 42 * would naively be expected. 43 * 44 * When no longer needed, the initialised |EVP_AEAD_CTX| structure must be 45 * passed to |EVP_AEAD_CTX_cleanup|, which will deallocate any memory used. 46 * 47 * With an |EVP_AEAD_CTX| in hand, one can seal and open messages. These 48 * operations are intended to meet the standard notions of privacy and 49 * authenticity for authenticated encryption. For formal definitions see 50 * Bellare and Namprempre, "Authenticated encryption: relations among notions 51 * and analysis of the generic composition paradigm," Lecture Notes in Computer 52 * Science B<1976> (2000), 531545, 53 * http://www-cse.ucsd.edu/~mihir/papers/oem.html. 54 * 55 * When sealing messages, a nonce must be given. The length of the nonce is 56 * fixed by the AEAD in use and is returned by |EVP_AEAD_nonce_length|. *The 57 * nonce must be unique for all messages with the same key*. This is critically 58 * important - nonce reuse may completely undermine the security of the AEAD. 59 * Nonces may be predictable and public, so long as they are unique. Uniqueness 60 * may be achieved with a simple counter or, if large enough, may be generated 61 * randomly. The nonce must be passed into the "open" operation by the receiver 62 * so must either be implicit (e.g. a counter), or must be transmitted along 63 * with the sealed message. 64 * 65 * The "seal" and "open" operations are atomic - an entire message must be 66 * encrypted or decrypted in a single call. Large messages may have to be split 67 * up in order to accomodate this. When doing so, be mindful of the need not to 68 * repeat nonces and the possibility that an attacker could duplicate, reorder 69 * or drop message chunks. For example, using a single key for a given (large) 70 * message and sealing chunks with nonces counting from zero would be secure as 71 * long as the number of chunks was securely transmitted. (Otherwise an 72 * attacker could truncate the message by dropping chunks from the end.) 73 * 74 * The number of chunks could be transmitted by prefixing it to the plaintext, 75 * for example. This also assumes that no other message would ever use the same 76 * key otherwise the rule that nonces must be unique for a given key would be 77 * violated. 78 * 79 * The "seal" and "open" operations also permit additional data to be 80 * authenticated via the |ad| parameter. This data is not included in the 81 * ciphertext and must be identical for both the "seal" and "open" call. This 82 * permits implicit context to be authenticated but may be empty if not needed. 83 * 84 * The "seal" and "open" operations may work in-place if the |out| and |in| 85 * arguments are equal. They may also be used to shift the data left inside the 86 * same buffer if |out| is less than |in|. However, |out| may not point inside 87 * the input data otherwise the input may be overwritten before it has been 88 * read. This situation will cause an error. 89 * 90 * The "seal" and "open" operations return one on success and zero on error. */ 91 92 93 /* AEAD algorithms. */ 94 95 /* EVP_aead_aes_128_gcm is AES-128 in Galois Counter Mode. */ 96 OPENSSL_EXPORT const EVP_AEAD *EVP_aead_aes_128_gcm(void); 97 98 /* EVP_aead_aes_256_gcm is AES-256 in Galois Counter Mode. */ 99 OPENSSL_EXPORT const EVP_AEAD *EVP_aead_aes_256_gcm(void); 100 101 /* EVP_aead_chacha20_poly1305 is an AEAD built from ChaCha20 and Poly1305. */ 102 OPENSSL_EXPORT const EVP_AEAD *EVP_aead_chacha20_poly1305(void); 103 104 /* EVP_aead_aes_128_key_wrap is AES-128 Key Wrap mode. This should never be 105 * used except to interoperate with existing systems that use this mode. 106 * 107 * If the nonce is emtpy then the default nonce will be used, otherwise it must 108 * be eight bytes long. The input must be a multiple of eight bytes long. No 109 * additional data can be given to this mode. */ 110 OPENSSL_EXPORT const EVP_AEAD *EVP_aead_aes_128_key_wrap(void); 111 112 /* EVP_aead_aes_256_key_wrap is AES-256 in Key Wrap mode. This should never be 113 * used except to interoperate with existing systems that use this mode. 114 * 115 * See |EVP_aead_aes_128_key_wrap| for details. */ 116 OPENSSL_EXPORT const EVP_AEAD *EVP_aead_aes_256_key_wrap(void); 117 118 /* EVP_has_aes_hardware returns one if we enable hardware support for fast and 119 * constant-time AES-GCM. */ 120 OPENSSL_EXPORT int EVP_has_aes_hardware(void); 121 122 123 /* TLS specific AEAD algorithms. 124 * 125 * These AEAD primitives do not meet the definition of generic AEADs. They are 126 * all specific to TLS in some fashion and should not be used outside of that 127 * context. */ 128 129 /* EVP_aead_rc4_md5_tls uses RC4 and HMAC(MD5) in MAC-then-encrypt mode. Unlike 130 * a standard AEAD, this is stateful as the RC4 state is carried from operation 131 * to operation. */ 132 OPENSSL_EXPORT const EVP_AEAD *EVP_aead_rc4_md5_tls(void); 133 134 135 /* Utility functions. */ 136 137 /* EVP_AEAD_key_length returns the length, in bytes, of the keys used by 138 * |aead|. */ 139 OPENSSL_EXPORT size_t EVP_AEAD_key_length(const EVP_AEAD *aead); 140 141 /* EVP_AEAD_nonce_length returns the length, in bytes, of the per-message nonce 142 * for |aead|. */ 143 OPENSSL_EXPORT size_t EVP_AEAD_nonce_length(const EVP_AEAD *aead); 144 145 /* EVP_AEAD_max_overhead returns the maximum number of additional bytes added 146 * by the act of sealing data with |aead|. */ 147 OPENSSL_EXPORT size_t EVP_AEAD_max_overhead(const EVP_AEAD *aead); 148 149 /* EVP_AEAD_max_tag_len returns the maximum tag length when using |aead|. This 150 * is the largest value that can be passed as |tag_len| to 151 * |EVP_AEAD_CTX_init|. */ 152 OPENSSL_EXPORT size_t EVP_AEAD_max_tag_len(const EVP_AEAD *aead); 153 154 155 /* AEAD operations. */ 156 157 /* An EVP_AEAD_CTX represents an AEAD algorithm configured with a specific key 158 * and message-independent IV. */ 159 typedef struct evp_aead_ctx_st { 160 const EVP_AEAD *aead; 161 /* aead_state is an opaque pointer to whatever state the AEAD needs to 162 * maintain. */ 163 void *aead_state; 164 } EVP_AEAD_CTX; 165 166 /* EVP_AEAD_MAX_OVERHEAD contains the maximum overhead used by any AEAD 167 * defined in this header. */ 168 #define EVP_AEAD_MAX_OVERHEAD 16 169 170 /* EVP_AEAD_DEFAULT_TAG_LENGTH is a magic value that can be passed to 171 * EVP_AEAD_CTX_init to indicate that the default tag length for an AEAD should 172 * be used. */ 173 #define EVP_AEAD_DEFAULT_TAG_LENGTH 0 174 175 /* EVP_AEAD_init initializes |ctx| for the given AEAD algorithm from |impl|. 176 * The |impl| argument may be NULL to choose the default implementation. 177 * Authentication tags may be truncated by passing a size as |tag_len|. A 178 * |tag_len| of zero indicates the default tag length and this is defined as 179 * EVP_AEAD_DEFAULT_TAG_LENGTH for readability. 180 * Returns 1 on success. Otherwise returns 0 and pushes to the error stack. */ 181 OPENSSL_EXPORT int EVP_AEAD_CTX_init(EVP_AEAD_CTX *ctx, const EVP_AEAD *aead, 182 const uint8_t *key, size_t key_len, 183 size_t tag_len, ENGINE *impl); 184 185 /* EVP_AEAD_CTX_cleanup frees any data allocated by |ctx|. */ 186 OPENSSL_EXPORT void EVP_AEAD_CTX_cleanup(EVP_AEAD_CTX *ctx); 187 188 /* EVP_AEAD_CTX_seal encrypts and authenticates |in_len| bytes from |in| and 189 * authenticates |ad_len| bytes from |ad| and writes the result to |out|. It 190 * returns one on success and zero otherwise. 191 * 192 * This function may be called (with the same |EVP_AEAD_CTX|) concurrently with 193 * itself or |EVP_AEAD_CTX_open|. 194 * 195 * At most |max_out_len| bytes are written to |out| and, in order to ensure 196 * success, |max_out_len| should be |in_len| plus the result of 197 * |EVP_AEAD_overhead|. On successful return, |*out_len| is set to the actual 198 * number of bytes written. 199 * 200 * The length of |nonce|, |nonce_len|, must be equal to the result of 201 * |EVP_AEAD_nonce_length| for this AEAD. 202 * 203 * |EVP_AEAD_CTX_seal| never results in a partial output. If |max_out_len| is 204 * insufficient, zero will be returned. (In this case, |*out_len| is set to 205 * zero.) 206 * 207 * If |in| and |out| alias then |out| must be <= |in|. */ 208 OPENSSL_EXPORT int EVP_AEAD_CTX_seal(const EVP_AEAD_CTX *ctx, uint8_t *out, 209 size_t *out_len, size_t max_out_len, 210 const uint8_t *nonce, size_t nonce_len, 211 const uint8_t *in, size_t in_len, 212 const uint8_t *ad, size_t ad_len); 213 214 /* EVP_AEAD_CTX_open authenticates |in_len| bytes from |in| and |ad_len| bytes 215 * from |ad| and decrypts at most |in_len| bytes into |out|. It returns one on 216 * success and zero otherwise. 217 * 218 * This function may be called (with the same |EVP_AEAD_CTX|) concurrently with 219 * itself or |EVP_AEAD_CTX_seal|. 220 * 221 * At most |in_len| bytes are written to |out|. In order to ensure success, 222 * |max_out_len| should be at least |in_len|. On successful return, |*out_len| 223 * is set to the the actual number of bytes written. 224 * 225 * The length of |nonce|, |nonce_len|, must be equal to the result of 226 * |EVP_AEAD_nonce_length| for this AEAD. 227 * 228 * |EVP_AEAD_CTX_open| never results in a partial output. If |max_out_len| is 229 * insufficient, zero will be returned. (In this case, |*out_len| is set to 230 * zero.) 231 * 232 * If |in| and |out| alias then |out| must be <= |in|. */ 233 OPENSSL_EXPORT int EVP_AEAD_CTX_open(const EVP_AEAD_CTX *ctx, uint8_t *out, 234 size_t *out_len, size_t max_out_len, 235 const uint8_t *nonce, size_t nonce_len, 236 const uint8_t *in, size_t in_len, 237 const uint8_t *ad, size_t ad_len); 238 239 240 #if defined(__cplusplus) 241 } /* extern C */ 242 #endif 243 244 #endif /* OPENSSL_HEADER_AEAD_H */ 245
