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Added generic EAX and CCM implementations.

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This commit is contained in:
Thomas Pornin 2017-10-23 23:27:28 +02:00
parent 8e94ad2fcb
commit dddc412922
14 changed files with 4530 additions and 13 deletions
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513
inc/bearssl_aead.h
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@ -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 +487,478 @@ 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 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 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 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 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