+/*
+ * 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 lengh 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.
+ */
+
+/**
+ * \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 additiona 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.
+ *
+ * \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.
+ *
+ * \param cc AEAD context structure.
+ * \param tag tag value to compare with (16 bytes).
+ * \return 1 on success (exact match of tag value), 0 otherwise.
+ */
+ uint32_t (*check_tag)(const br_aead_class **cc, const void *tag);
+};
+
+/**
+ * \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 additiona 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 Class instance for GCM.
+ */
+extern const br_aead_class br_gcm_vtable;
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
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