/*
* Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#ifndef BR_BEARSSL_AEAD_H__
#define BR_BEARSSL_AEAD_H__
#include <stddef.h>
#include <stdint.h>
#include "bearssl_block.h"
#include "bearssl_hash.h"
#ifdef __cplusplus
extern "C" {
#endif
/** \file bearssl_aead.h
*
* # Authenticated Encryption with Additional Data
*
* This file documents the API for AEAD encryption.
*
*
* ## Procedural API
*
* An AEAD algorithm processes messages and provides confidentiality
* (encryption) and checked integrity (MAC). It uses the following
* parameters:
*
* - A symmetric key. Exact size depends on the AEAD algorithm.
*
* - A nonce (IV). Size depends on the AEAD algorithm; for most
* algorithms, it is crucial for security that any given nonce
* value is never used twice for the same key and distinct
* messages.
*
* - Data to encrypt and protect.
*
* - Additional authenticated data, which is covered by the MAC but
* otherwise left untouched (i.e. not encrypted).
*
* The AEAD algorithm encrypts the data, and produces an authentication
* tag. It is assumed that the encrypted data, the tag, the additional
* authenticated data and the nonce are sent to the receiver; the
* additional data and the nonce may be implicit (e.g. using elements of
* the underlying transport protocol, such as record sequence numbers).
* The receiver will recompute the tag value and compare it with the one
* received; if they match, then the data is correct, and can be
* decrypted and used; otherwise, at least one of the elements was
* altered in transit, normally leading to wholesale rejection of the
* complete message.
*
* For each AEAD algorithm, identified by a symbolic name (hereafter
* denoted as "`xxx`"), the following functions are defined:
*
* - `br_xxx_init()`
*
* Initialise the AEAD algorithm, on a provided context structure.
* Exact parameters depend on the algorithm, and may include
* pointers to extra implementations and context structures. The
* secret key is provided at this point, either directly or
* indirectly.
*
* - `br_xxx_reset()`
*
* Start a new AEAD computation. The nonce value is provided as
* parameter to this function.
*
* - `br_xxx_aad_inject()`
*
* Inject some additional authenticated data. Additional data may
* be provided in several chunks of arbitrary length.
*
* - `br_xxx_flip()`
*
* This function MUST be called after injecting all additional
* authenticated data, and before beginning to encrypt the plaintext
* (or decrypt the ciphertext).
*
* - `br_xxx_run()`
*
* Process some plaintext (to encrypt) or ciphertext (to decrypt).
* Encryption/decryption is done in place. Data may be provided in
* several chunks of arbitrary length.
*
* - `br_xxx_get_tag()`
*
* Compute the authentication tag. All message data (encrypted or
* decrypted) must have been injected at that point. Also, this
* call may modify internal context elements, so it may be called
* only once for a given AEAD computation.
*
* - `br_xxx_check_tag()`
*
* An alternative to `br_xxx_get_tag()`, meant to be used by the
* receiver: the authentication tag is internally recomputed, and
* compared with the one provided as parameter.
*
* This API makes the following assumptions on the AEAD algorithm:
*
* - Encryption does not expand the size of the ciphertext; there is
* no padding. This is true of most modern AEAD modes such as GCM.
*
* - The additional authenticated data must be processed first,
* before the encrypted/decrypted data.
*
* - Nonce, plaintext and additional authenticated data all consist
* in an integral number of bytes. There is no provision to use
* 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
* way to report invalid usage; it is up to the caller to ensure that
* the provided key, nonce, and data elements all fit the algorithm's
* requirements.
*
*
* ## Object-Oriented API
*
* Each context structure begins with a field (called `vtable`) that
* points to an instance of a structure that references the relevant
* functions through pointers. Each such structure contains the
* following:
*
* - `reset`
*
* Pointer to the reset function, that allows starting a new
* computation.
*
* - `aad_inject`
*
* Pointer to the additional authenticated data injection function.
*
* - `flip`
*
* Pointer to the function that transitions from additional data
* to main message data processing.
*
* - `get_tag`
*
* Pointer to the function that computes and returns the tag.
*
* - `check_tag`
*
* Pointer to the function that computes and verifies the tag against
* a received value.
*
* 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).
*/
/**
* \brief Class type of an AEAD algorithm.
*/
typedef struct br_aead_class_ br_aead_class;
struct br_aead_class_ {
/**
* \brief Size (in bytes) of authentication tags created by
* this AEAD algorithm.
*/
size_t tag_size;
/**
* \brief Reset an AEAD context.
*
* This function resets an already initialised AEAD context for
* a new computation run. Implementations and keys are
* conserved. This function can be called at any time; it
* cancels any ongoing AEAD computation that uses the provided
* context structure.
* The provided IV is a _nonce_. Each AEAD algorithm has its
* own requirements on IV size and contents; for most of them,
* it is crucial to security that each nonce value is used
* only once for a given secret key.
*
* \param cc AEAD context structure.
* \param iv AEAD nonce to use.
* \param len AEAD nonce length (in bytes).
*/
void (*reset)(const br_aead_class **cc, const void *iv, size_t len);
/**
* \brief Inject additional authenticated data.
*
* The provided data is injected into a running AEAD
* computation. Additional data must be injected _before_ the
* call to `flip()`. Additional data can be injected in several
* chunks of arbitrary length.
*
* \param cc AEAD context structure.
* \param data pointer to additional authenticated data.
* \param len length of additional authenticated data (in bytes).
*/
void (*aad_inject)(const br_aead_class **cc,
const void *data, size_t len);
/**
* \brief Finish injection of additional authenticated data.
*
* This function MUST be called before beginning the actual
* encryption or decryption (with `run()`), even if no
* additional authenticated data was injected. No additional
* authenticated data may be injected after this function call.
*
* \param cc AEAD context structure.
*/
void (*flip)(const br_aead_class **cc);
/**
* \brief Encrypt or decrypt some data.
*
* Data encryption or decryption can be done after `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 cc AEAD 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 (*run)(const br_aead_class **cc, int encrypt,
void *data, size_t len);
/**
* \brief Compute authentication tag.
*
* Compute the AEAD authentication tag. The tag length depends
* on the AEAD algorithm; it is written in the provided `tag`
* buffer. This call terminates the AEAD run: no data may be
* processed with that AEAD context afterwards, until `reset()`
* is called to initiate a new AEAD 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
* `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.
*/
void (*get_tag)(const br_aead_class **cc, void *tag);
/**
* \brief Compute and check authentication tag.
*
* This function is an alternative to `get_tag()`, and is
* normally used on the receiving end (i.e. when decrypting
* messages). 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 depends on the AEAD algorithm.
*
* \param cc AEAD context structure.
* \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);
};
/**
* \brief Context structure for GCM.
*
* GCM is an AEAD mode that combines a block cipher in CTR mode with a
* MAC based on GHASH, to provide authenticated encryption:
*
* - Any block cipher with 16-byte blocks can be used with GCM.
*
* - The nonce can have any length, from 0 up to 2^64-1 bits; however,
* 96-bit nonces (12 bytes) are recommended (nonces with a length
* distinct from 12 bytes are internally hashed, which risks reusing
* nonce value with a small but not always negligible probability).
*
* - Additional authenticated data may have length up to 2^64-1 bits.
*
* - Message length may range up to 2^39-256 bits at most.
*
* - The authentication tag has length 16 bytes.
*
* The GCM 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
* GCM 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_ctr_class **bctx;
br_ghash gh;
unsigned char h[16];
unsigned char j0_1[12];
unsigned char buf[16];
unsigned char y[16];
uint32_t j0_2, jc;
uint64_t count_aad, count_ctr;
#endif
} br_gcm_context;
/**
* \brief Initialize a GCM context.
*
* A block cipher implementation, with its initialised context structure,
* is provided. The block cipher MUST use 16-byte blocks in CTR mode,
* and its secret key MUST have been already set in the provided context.
* A GHASH implementation must also be provided. The parameters are linked
* in the GCM context.
*
* After this function has been called, the `br_gcm_reset()` function must
* be called, to provide the IV for GCM computation.
*
* \param ctx GCM context structure.
* \param bctx block cipher context (already initialised with secret key).
* \param gh GHASH implementation.
*/
void br_gcm_init(br_gcm_context *ctx,
const br_block_ctr_class **bctx, br_ghash gh);
/**
* \brief Reset a GCM context.
*
* This function resets an already initialised GCM context for a new
* computation run. Implementations and keys are conserved. This function
* can be called at any time; it cancels any ongoing GCM computation that
* uses the provided context structure.
*
* The provided IV is a _nonce_. It is critical to GCM security that IV
* values are not repeated for the same encryption key. IV can have
* arbitrary length (up to 2^64-1 bits), but the "normal" length is
* 96 bits (12 bytes).
*
* \param ctx GCM context structure.
* \param iv GCM nonce to use.
* \param len GCM nonce length (in bytes).
*/
void br_gcm_reset(br_gcm_context *ctx, const void *iv, size_t len);
/**
* \brief Inject additional authenticated data into GCM.
*
* The provided data is injected into a running GCM computation. Additional
* data must be injected _before_ the call to `br_gcm_flip()`.
* Additional data can be injected in several chunks of arbitrary length;
* the maximum total size of additional authenticated data is 2^64-1
* bits.
*
* \param ctx GCM context structure.
* \param data pointer to additional authenticated data.
* \param len length of additional authenticated data (in bytes).
*/
void br_gcm_aad_inject(br_gcm_context *ctx, const void *data, size_t len);
/**
* \brief Finish injection of additional authenticated data into GCM.
*
* This function MUST be called before beginning the actual encryption
* or decryption (with `br_gcm_run()`), even if no additional authenticated
* data was injected. No additional authenticated data may be injected
* after this function call.
*
* \param ctx GCM context structure.
*/
void br_gcm_flip(br_gcm_context *ctx);
/**
* \brief Encrypt or decrypt some data with GCM.
*
* Data encryption or decryption can be done after `br_gcm_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. The maximum
* total length for data is 2^39-256 bits, i.e. about 65 gigabytes.
*
* \param ctx GCM 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_gcm_run(br_gcm_context *ctx, int encrypt, void *data, size_t len);
/**
* \brief Compute GCM authentication tag.
*
* Compute the GCM authentication tag. The tag is a 16-byte value which
* 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()` function can be used to
* compute and check the tag value.
*
* \param ctx GCM context structure.
* \param tag destination buffer for the tag (16 bytes).
*/
void br_gcm_get_tag(br_gcm_context *ctx, void *tag);
/**
* \brief Compute and check GCM authentication tag.
*
* This function is an alternative to `br_gcm_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 GCM 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_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 between 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
#endif