X-Git-Url: https://www.bearssl.org/gitweb//home/git/?p=BearSSL;a=blobdiff_plain;f=inc%2Fbearssl_aead.h;h=c495dc20dbb2e1198520764cbea122fb386b5696;hp=09cb9e891b33ed3f50213d9e39c96b3cd461b302;hb=12db697bccf2ff732665b9c7668c0826513489e0;hpb=127fb4a31d24e58fa8e04a154c6e87a2cb28245b diff --git a/inc/bearssl_aead.h b/inc/bearssl_aead.h index 09cb9e8..c495dc2 100644 --- a/inc/bearssl_aead.h +++ b/inc/bearssl_aead.h @@ -127,7 +127,7 @@ extern "C" { * * - Nonce, plaintext and additional authenticated data all consist * in an integral number of bytes. There is no provision to use - * elements whose lengh in bits is not a multiple of 8. + * elements whose length in bits is not a multiple of 8. * * Each AEAD algorithm has its own requirements and limits on the sizes * of additional data and plaintext. This API does not provide any @@ -169,6 +169,9 @@ extern "C" { * Note that there is no OOP method for context initialisation: the * various AEAD algorithms have different requirements that would not * map well to a single initialisation API. + * + * The OOP API is not provided for CCM, due to its specific requirements + * (length of plaintext must be known in advance). */ /** @@ -213,7 +216,7 @@ struct br_aead_class_ { * * \param cc AEAD context structure. * \param data pointer to additional authenticated data. - * \param len length of additiona authenticated data (in bytes). + * \param len length of additional authenticated data (in bytes). */ void (*aad_inject)(const br_aead_class **cc, const void *data, size_t len); @@ -266,6 +269,8 @@ struct br_aead_class_ { * `check_tag()` function may be used to compute and check the * tag value. * + * Tag length depends on the AEAD algorithm. + * * \param cc AEAD context structure. * \param tag destination buffer for the tag. */ @@ -282,11 +287,44 @@ struct br_aead_class_ { * data or the tag was altered in transit, normally leading to * wholesale rejection of the complete message. * + * Tag length depends on the AEAD algorithm. + * * \param cc AEAD context structure. - * \param tag tag value to compare with (16 bytes). + * \param tag tag value to compare with. * \return 1 on success (exact match of tag value), 0 otherwise. */ uint32_t (*check_tag)(const br_aead_class **cc, const void *tag); + + /** + * \brief Compute authentication tag (with truncation). + * + * This function is similar to `get_tag()`, except that the tag + * length is provided. Some AEAD algorithms allow several tag + * lengths, usually by truncating the normal tag. Shorter tags + * mechanically increase success probability of forgeries. + * The range of allowed tag lengths depends on the algorithm. + * + * \param cc AEAD context structure. + * \param tag destination buffer for the tag. + * \param len tag length (in bytes). + */ + void (*get_tag_trunc)(const br_aead_class **cc, void *tag, size_t len); + + /** + * \brief Compute and check authentication tag (with truncation). + * + * This function is similar to `check_tag()` except that it + * works over an explicit tag length. See `get_tag()` for a + * discussion of explicit tag lengths; the range of allowed tag + * lengths depends on the algorithm. + * + * \param cc AEAD context structure. + * \param tag tag value to compare with. + * \param len tag length (in bytes). + * \return 1 on success (exact match of tag value), 0 otherwise. + */ + uint32_t (*check_tag_trunc)(const br_aead_class **cc, + const void *tag, size_t len); }; /** @@ -379,7 +417,7 @@ void br_gcm_reset(br_gcm_context *ctx, const void *iv, size_t len); * * \param ctx GCM context structure. * \param data pointer to additional authenticated data. - * \param len length of additiona authenticated data (in bytes). + * \param len length of additional authenticated data (in bytes). */ void br_gcm_aad_inject(br_gcm_context *ctx, const void *data, size_t len); @@ -449,11 +487,571 @@ void br_gcm_get_tag(br_gcm_context *ctx, void *tag); */ uint32_t br_gcm_check_tag(br_gcm_context *ctx, const void *tag); +/** + * \brief Compute GCM authentication tag (with truncation). + * + * This function is similar to `br_gcm_get_tag()`, except that it allows + * the tag to be truncated to a smaller length. The intended tag length + * is provided as `len` (in bytes); it MUST be no more than 16, but + * it may be smaller. Note that decreasing tag length mechanically makes + * forgeries easier; NIST SP 800-38D specifies that the tag length shall + * lie between 12 and 16 bytes (inclusive), but may be truncated down to + * 4 or 8 bytes, for specific applications that can tolerate it. It must + * also be noted that successful forgeries leak information on the + * authentication key, making subsequent forgeries easier. Therefore, + * tag truncation, and in particular truncation to sizes lower than 12 + * bytes, shall be envisioned only with great care. + * + * The tag is written in the provided `tag` buffer. This call terminates + * the GCM run: no data may be processed with that GCM context + * afterwards, until `br_gcm_reset()` is called to initiate a new GCM + * run. + * + * The tag value must normally be sent along with the encrypted data. + * When decrypting, the tag value must be recomputed and compared with + * the received tag: if the two tag values differ, then either the tag + * or the encrypted data was altered in transit. As an alternative to + * this function, the `br_gcm_check_tag_trunc()` function can be used to + * compute and check the tag value. + * + * \param ctx GCM context structure. + * \param tag destination buffer for the tag. + * \param len tag length (16 bytes or less). + */ +void br_gcm_get_tag_trunc(br_gcm_context *ctx, void *tag, size_t len); + +/** + * \brief Compute and check GCM authentication tag (with truncation). + * + * This function is an alternative to `br_gcm_get_tag_trunc()`, normally used + * on the receiving end (i.e. when decrypting value). The tag value is + * recomputed and compared with the provided tag value. If they match, 1 + * is returned; on mismatch, 0 is returned. A returned value of 0 means + * that the data or the tag was altered in transit, normally leading to + * wholesale rejection of the complete message. + * + * Tag length MUST be 16 bytes or less. The normal GCM tag length is 16 + * bytes. See `br_check_tag_trunc()` for some discussion on the potential + * perils of truncating authentication tags. + * + * \param ctx GCM context structure. + * \param tag tag value to compare with. + * \param len tag length (in bytes). + * \return 1 on success (exact match of tag value), 0 otherwise. + */ +uint32_t br_gcm_check_tag_trunc(br_gcm_context *ctx, + const void *tag, size_t len); + /** * \brief Class instance for GCM. */ extern const br_aead_class br_gcm_vtable; +/** + * \brief Context structure for EAX. + * + * EAX is an AEAD mode that combines a block cipher in CTR mode with + * CBC-MAC using the same block cipher and the same key, to provide + * authenticated encryption: + * + * - Any block cipher with 16-byte blocks can be used with EAX + * (technically, other block sizes are defined as well, but this + * is not implemented by these functions; shorter blocks also + * imply numerous security issues). + * + * - The nonce can have any length, as long as nonce values are + * not reused (thus, if nonces are randomly selected, the nonce + * size should be such that reuse probability is negligible). + * + * - Additional authenticated data length is unlimited. + * + * - Message length is unlimited. + * + * - The authentication tag has length 16 bytes. + * + * The EAX initialisation function receives as parameter an + * _initialised_ block cipher implementation context, with the secret + * key already set. A pointer to that context will be kept within the + * EAX context structure. It is up to the caller to allocate and + * initialise that block cipher context. + */ +typedef struct { + /** \brief Pointer to vtable for this context. */ + const br_aead_class *vtable; + +#ifndef BR_DOXYGEN_IGNORE + const br_block_ctrcbc_class **bctx; + unsigned char L2[16]; + unsigned char L4[16]; + unsigned char nonce[16]; + unsigned char head[16]; + unsigned char ctr[16]; + unsigned char cbcmac[16]; + unsigned char buf[16]; + size_t ptr; +#endif +} br_eax_context; + +/** + * \brief EAX captured state. + * + * Some internal values computed by EAX may be captured at various + * points, and reused for another EAX run with the same secret key, + * for lower per-message overhead. Captured values do not depend on + * the nonce. + */ +typedef struct { +#ifndef BR_DOXYGEN_IGNORE + unsigned char st[3][16]; +#endif +} br_eax_state; + +/** + * \brief Initialize an EAX context. + * + * A block cipher implementation, with its initialised context + * structure, is provided. The block cipher MUST use 16-byte blocks in + * CTR + CBC-MAC mode, and its secret key MUST have been already set in + * the provided context. The parameters are linked in the EAX context. + * + * After this function has been called, the `br_eax_reset()` function must + * be called, to provide the nonce for EAX computation. + * + * \param ctx EAX context structure. + * \param bctx block cipher context (already initialised with secret key). + */ +void br_eax_init(br_eax_context *ctx, const br_block_ctrcbc_class **bctx); + +/** + * \brief Capture pre-AAD state. + * + * This function precomputes key-dependent data, and stores it in the + * provided `st` structure. This structure should then be used with + * `br_eax_reset_pre_aad()`, or updated with `br_eax_get_aad_mac()` + * and then used with `br_eax_reset_post_aad()`. + * + * The EAX context structure is unmodified by this call. + * + * \param ctx EAX context structure. + * \param st recipient for captured state. + */ +void br_eax_capture(const br_eax_context *ctx, br_eax_state *st); + +/** + * \brief Reset an EAX context. + * + * This function resets an already initialised EAX context for a new + * computation run. Implementations and keys are conserved. This function + * can be called at any time; it cancels any ongoing EAX computation that + * uses the provided context structure. + * + * It is critical to EAX security that nonce values are not repeated for + * the same encryption key. Nonces can have arbitrary length. If nonces + * are randomly generated, then a nonce length of at least 128 bits (16 + * bytes) is recommended, to make nonce reuse probability sufficiently + * low. + * + * \param ctx EAX context structure. + * \param nonce EAX nonce to use. + * \param len EAX nonce length (in bytes). + */ +void br_eax_reset(br_eax_context *ctx, const void *nonce, size_t len); + +/** + * \brief Reset an EAX context with a pre-AAD captured state. + * + * This function is an alternative to `br_eax_reset()`, that reuses a + * previously captured state structure for lower per-message overhead. + * The state should have been populated with `br_eax_capture_state()` + * but not updated with `br_eax_get_aad_mac()`. + * + * After this function is called, additional authenticated data MUST + * be injected. At least one byte of additional authenticated data + * MUST be provided with `br_eax_aad_inject()`; computation result will + * be incorrect if `br_eax_flip()` is called right away. + * + * After injection of the AAD and call to `br_eax_flip()`, at least + * one message byte must be provided. Empty messages are not supported + * with this reset mode. + * + * \param ctx EAX context structure. + * \param st pre-AAD captured state. + * \param nonce EAX nonce to use. + * \param len EAX nonce length (in bytes). + */ +void br_eax_reset_pre_aad(br_eax_context *ctx, const br_eax_state *st, + const void *nonce, size_t len); + +/** + * \brief Reset an EAX context with a post-AAD captured state. + * + * This function is an alternative to `br_eax_reset()`, that reuses a + * previously captured state structure for lower per-message overhead. + * The state should have been populated with `br_eax_capture_state()` + * and then updated with `br_eax_get_aad_mac()`. + * + * After this function is called, message data MUST be injected. The + * `br_eax_flip()` function MUST NOT be called. At least one byte of + * message data MUST be provided with `br_eax_run()`; empty messages + * are not supported with this reset mode. + * + * \param ctx EAX context structure. + * \param st post-AAD captured state. + * \param nonce EAX nonce to use. + * \param len EAX nonce length (in bytes). + */ +void br_eax_reset_post_aad(br_eax_context *ctx, const br_eax_state *st, + const void *nonce, size_t len); + +/** + * \brief Inject additional authenticated data into EAX. + * + * The provided data is injected into a running EAX computation. Additional + * data must be injected _before_ the call to `br_eax_flip()`. + * Additional data can be injected in several chunks of arbitrary length; + * the total amount of additional authenticated data is unlimited. + * + * \param ctx EAX context structure. + * \param data pointer to additional authenticated data. + * \param len length of additional authenticated data (in bytes). + */ +void br_eax_aad_inject(br_eax_context *ctx, const void *data, size_t len); + +/** + * \brief Finish injection of additional authenticated data into EAX. + * + * This function MUST be called before beginning the actual encryption + * or decryption (with `br_eax_run()`), even if no additional authenticated + * data was injected. No additional authenticated data may be injected + * after this function call. + * + * \param ctx EAX context structure. + */ +void br_eax_flip(br_eax_context *ctx); + +/** + * \brief Obtain a copy of the MAC on additional authenticated data. + * + * This function may be called only after `br_eax_flip()`; it copies the + * AAD-specific MAC value into the provided state. The MAC value depends + * on the secret key and the additional data itself, but not on the + * nonce. The updated state `st` is meant to be used as parameter for a + * further `br_eax_reset_post_aad()` call. + * + * \param ctx EAX context structure. + * \param st captured state to update. + */ +static inline void +br_eax_get_aad_mac(const br_eax_context *ctx, br_eax_state *st) +{ + memcpy(st->st[1], ctx->head, sizeof ctx->head); +} + +/** + * \brief Encrypt or decrypt some data with EAX. + * + * Data encryption or decryption can be done after `br_eax_flip()` + * has been called on the context. If `encrypt` is non-zero, then the + * provided data shall be plaintext, and it is encrypted in place. + * Otherwise, the data shall be ciphertext, and it is decrypted in place. + * + * Data may be provided in several chunks of arbitrary length. + * + * \param ctx EAX context structure. + * \param encrypt non-zero for encryption, zero for decryption. + * \param data data to encrypt or decrypt. + * \param len data length (in bytes). + */ +void br_eax_run(br_eax_context *ctx, int encrypt, void *data, size_t len); + +/** + * \brief Compute EAX authentication tag. + * + * Compute the EAX authentication tag. The tag is a 16-byte value which + * is written in the provided `tag` buffer. This call terminates the + * EAX run: no data may be processed with that EAX context afterwards, + * until `br_eax_reset()` is called to initiate a new EAX run. + * + * The tag value must normally be sent along with the encrypted data. + * When decrypting, the tag value must be recomputed and compared with + * the received tag: if the two tag values differ, then either the tag + * or the encrypted data was altered in transit. As an alternative to + * this function, the `br_eax_check_tag()` function can be used to + * compute and check the tag value. + * + * \param ctx EAX context structure. + * \param tag destination buffer for the tag (16 bytes). + */ +void br_eax_get_tag(br_eax_context *ctx, void *tag); + +/** + * \brief Compute and check EAX authentication tag. + * + * This function is an alternative to `br_eax_get_tag()`, normally used + * on the receiving end (i.e. when decrypting value). The tag value is + * recomputed and compared with the provided tag value. If they match, 1 + * is returned; on mismatch, 0 is returned. A returned value of 0 means + * that the data or the tag was altered in transit, normally leading to + * wholesale rejection of the complete message. + * + * \param ctx EAX context structure. + * \param tag tag value to compare with (16 bytes). + * \return 1 on success (exact match of tag value), 0 otherwise. + */ +uint32_t br_eax_check_tag(br_eax_context *ctx, const void *tag); + +/** + * \brief Compute EAX authentication tag (with truncation). + * + * This function is similar to `br_eax_get_tag()`, except that it allows + * the tag to be truncated to a smaller length. The intended tag length + * is provided as `len` (in bytes); it MUST be no more than 16, but + * it may be smaller. Note that decreasing tag length mechanically makes + * forgeries easier; NIST SP 800-38D specifies that the tag length shall + * lie between 12 and 16 bytes (inclusive), but may be truncated down to + * 4 or 8 bytes, for specific applications that can tolerate it. It must + * also be noted that successful forgeries leak information on the + * authentication key, making subsequent forgeries easier. Therefore, + * tag truncation, and in particular truncation to sizes lower than 12 + * bytes, shall be envisioned only with great care. + * + * The tag is written in the provided `tag` buffer. This call terminates + * the EAX run: no data may be processed with that EAX context + * afterwards, until `br_eax_reset()` is called to initiate a new EAX + * run. + * + * The tag value must normally be sent along with the encrypted data. + * When decrypting, the tag value must be recomputed and compared with + * the received tag: if the two tag values differ, then either the tag + * or the encrypted data was altered in transit. As an alternative to + * this function, the `br_eax_check_tag_trunc()` function can be used to + * compute and check the tag value. + * + * \param ctx EAX context structure. + * \param tag destination buffer for the tag. + * \param len tag length (16 bytes or less). + */ +void br_eax_get_tag_trunc(br_eax_context *ctx, void *tag, size_t len); + +/** + * \brief Compute and check EAX authentication tag (with truncation). + * + * This function is an alternative to `br_eax_get_tag_trunc()`, normally used + * on the receiving end (i.e. when decrypting value). The tag value is + * recomputed and compared with the provided tag value. If they match, 1 + * is returned; on mismatch, 0 is returned. A returned value of 0 means + * that the data or the tag was altered in transit, normally leading to + * wholesale rejection of the complete message. + * + * Tag length MUST be 16 bytes or less. The normal EAX tag length is 16 + * bytes. See `br_check_tag_trunc()` for some discussion on the potential + * perils of truncating authentication tags. + * + * \param ctx EAX context structure. + * \param tag tag value to compare with. + * \param len tag length (in bytes). + * \return 1 on success (exact match of tag value), 0 otherwise. + */ +uint32_t br_eax_check_tag_trunc(br_eax_context *ctx, + const void *tag, size_t len); + +/** + * \brief Class instance for EAX. + */ +extern const br_aead_class br_eax_vtable; + +/** + * \brief Context structure for CCM. + * + * CCM is an AEAD mode that combines a block cipher in CTR mode with + * CBC-MAC using the same block cipher and the same key, to provide + * authenticated encryption: + * + * - Any block cipher with 16-byte blocks can be used with CCM + * (technically, other block sizes are defined as well, but this + * is not implemented by these functions; shorter blocks also + * imply numerous security issues). + * + * - The authentication tag length, and plaintext length, MUST be + * known when starting processing data. Plaintext and ciphertext + * can still be provided by chunks, but the total size must match + * the value provided upon initialisation. + * + * - The nonce length is constrained betwen 7 and 13 bytes (inclusive). + * Furthermore, the plaintext length, when encoded, must fit over + * 15-nonceLen bytes; thus, if the nonce has length 13 bytes, then + * the plaintext length cannot exceed 65535 bytes. + * + * - Additional authenticated data length is practically unlimited + * (formal limit is at 2^64 bytes). + * + * - The authentication tag has length 4 to 16 bytes (even values only). + * + * The CCM initialisation function receives as parameter an + * _initialised_ block cipher implementation context, with the secret + * key already set. A pointer to that context will be kept within the + * CCM context structure. It is up to the caller to allocate and + * initialise that block cipher context. + */ +typedef struct { +#ifndef BR_DOXYGEN_IGNORE + const br_block_ctrcbc_class **bctx; + unsigned char ctr[16]; + unsigned char cbcmac[16]; + unsigned char tagmask[16]; + unsigned char buf[16]; + size_t ptr; + size_t tag_len; +#endif +} br_ccm_context; + +/** + * \brief Initialize a CCM context. + * + * A block cipher implementation, with its initialised context + * structure, is provided. The block cipher MUST use 16-byte blocks in + * CTR + CBC-MAC mode, and its secret key MUST have been already set in + * the provided context. The parameters are linked in the CCM context. + * + * After this function has been called, the `br_ccm_reset()` function must + * be called, to provide the nonce for CCM computation. + * + * \param ctx CCM context structure. + * \param bctx block cipher context (already initialised with secret key). + */ +void br_ccm_init(br_ccm_context *ctx, const br_block_ctrcbc_class **bctx); + +/** + * \brief Reset a CCM context. + * + * This function resets an already initialised CCM context for a new + * computation run. Implementations and keys are conserved. This function + * can be called at any time; it cancels any ongoing CCM computation that + * uses the provided context structure. + * + * The `aad_len` parameter contains the total length, in bytes, of the + * additional authenticated data. It may be zero. That length MUST be + * exact. + * + * The `data_len` parameter contains the total length, in bytes, of the + * data that will be injected (plaintext or ciphertext). That length MUST + * be exact. Moreover, that length MUST be less than 2^(8*(15-nonce_len)). + * + * The nonce length (`nonce_len`), in bytes, must be in the 7..13 range + * (inclusive). + * + * The tag length (`tag_len`), in bytes, must be in the 4..16 range, and + * be an even integer. Short tags mechanically allow for higher forgery + * probabilities; hence, tag sizes smaller than 12 bytes shall be used only + * with care. + * + * It is critical to CCM security that nonce values are not repeated for + * the same encryption key. Random generation of nonces is not generally + * recommended, due to the relatively small maximum nonce value. + * + * Returned value is 1 on success, 0 on error. An error is reported if + * the tag or nonce length is out of range, or if the + * plaintext/ciphertext length cannot be encoded with the specified + * nonce length. + * + * \param ctx CCM context structure. + * \param nonce CCM nonce to use. + * \param nonce_len CCM nonce length (in bytes, 7 to 13). + * \param aad_len additional authenticated data length (in bytes). + * \param data_len plaintext/ciphertext length (in bytes). + * \param tag_len tag length (in bytes). + * \return 1 on success, 0 on error. + */ +int br_ccm_reset(br_ccm_context *ctx, const void *nonce, size_t nonce_len, + uint64_t aad_len, uint64_t data_len, size_t tag_len); + +/** + * \brief Inject additional authenticated data into CCM. + * + * The provided data is injected into a running CCM computation. Additional + * data must be injected _before_ the call to `br_ccm_flip()`. + * Additional data can be injected in several chunks of arbitrary length, + * but the total amount MUST exactly match the value which was provided + * to `br_ccm_reset()`. + * + * \param ctx CCM context structure. + * \param data pointer to additional authenticated data. + * \param len length of additional authenticated data (in bytes). + */ +void br_ccm_aad_inject(br_ccm_context *ctx, const void *data, size_t len); + +/** + * \brief Finish injection of additional authenticated data into CCM. + * + * This function MUST be called before beginning the actual encryption + * or decryption (with `br_ccm_run()`), even if no additional authenticated + * data was injected. No additional authenticated data may be injected + * after this function call. + * + * \param ctx CCM context structure. + */ +void br_ccm_flip(br_ccm_context *ctx); + +/** + * \brief Encrypt or decrypt some data with CCM. + * + * Data encryption or decryption can be done after `br_ccm_flip()` + * has been called on the context. If `encrypt` is non-zero, then the + * provided data shall be plaintext, and it is encrypted in place. + * Otherwise, the data shall be ciphertext, and it is decrypted in place. + * + * Data may be provided in several chunks of arbitrary length, provided + * that the total length exactly matches the length provided to the + * `br_ccm_reset()` call. + * + * \param ctx CCM context structure. + * \param encrypt non-zero for encryption, zero for decryption. + * \param data data to encrypt or decrypt. + * \param len data length (in bytes). + */ +void br_ccm_run(br_ccm_context *ctx, int encrypt, void *data, size_t len); + +/** + * \brief Compute CCM authentication tag. + * + * Compute the CCM authentication tag. This call terminates the CCM + * run: all data must have been injected with `br_ccm_run()` (in zero, + * one or more successive calls). After this function has been called, + * no more data can br processed; a `br_ccm_reset()` call is required + * to start a new message. + * + * The tag length was provided upon context initialisation (last call + * to `br_ccm_reset()`); it is returned by this function. + * + * The tag value must normally be sent along with the encrypted data. + * When decrypting, the tag value must be recomputed and compared with + * the received tag: if the two tag values differ, then either the tag + * or the encrypted data was altered in transit. As an alternative to + * this function, the `br_ccm_check_tag()` function can be used to + * compute and check the tag value. + * + * \param ctx CCM context structure. + * \param tag destination buffer for the tag (up to 16 bytes). + * \return the tag length (in bytes). + */ +size_t br_ccm_get_tag(br_ccm_context *ctx, void *tag); + +/** + * \brief Compute and check CCM authentication tag. + * + * This function is an alternative to `br_ccm_get_tag()`, normally used + * on the receiving end (i.e. when decrypting value). The tag value is + * recomputed and compared with the provided tag value. If they match, 1 + * is returned; on mismatch, 0 is returned. A returned value of 0 means + * that the data or the tag was altered in transit, normally leading to + * wholesale rejection of the complete message. + * + * \param ctx CCM context structure. + * \param tag tag value to compare with (up to 16 bytes). + * \return 1 on success (exact match of tag value), 0 otherwise. + */ +uint32_t br_ccm_check_tag(br_ccm_context *ctx, const void *tag); + #ifdef __cplusplus } #endif