Accelerated GCM AES-128 Cipher
Cryptography Hardware Acceleration Plugins > Silicon Labs Cryptography Hardware Acceleration Plugins for mbed TLS

Detailed Description

Accelerated AES-GCM-128 cipher for the mbed TLS API using the CRYPTOACC or SE peripheral.

This module implements the GCM AES-128 cipher, as defined in D. McGrew, J. Viega, The Galois/Counter Mode of Operation (GCM), Natl. Inst. Stand. Technol. For more information on GCM, see NIST SP 800-38D: Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC.

Data Structures

struct  mbedtls_gcm_context
 The GCM context structure.
 

Macros

#define MBEDTLS_GCM_ENCRYPT   1
 
#define MBEDTLS_GCM_DECRYPT   0
 
#define MBEDTLS_ERR_GCM_AUTH_FAILED   -0x0012
 
#define MBEDTLS_ERR_GCM_HW_ACCEL_FAILED   -0x0013
 
#define MBEDTLS_ERR_GCM_BAD_INPUT   -0x0014
 

Functions

void mbedtls_gcm_init (mbedtls_gcm_context *ctx)
 This function initializes the specified GCM context, to make references valid, and prepares the context for mbedtls_gcm_setkey() or mbedtls_gcm_free().
 
int mbedtls_gcm_setkey (mbedtls_gcm_context *ctx, mbedtls_cipher_id_t cipher, const unsigned char *key, unsigned int keybits)
 This function associates a GCM context with a cipher algorithm and a key.
 
int mbedtls_gcm_crypt_and_tag (mbedtls_gcm_context *ctx, int mode, size_t length, const unsigned char *iv, size_t iv_len, const unsigned char *add, size_t add_len, const unsigned char *input, unsigned char *output, size_t tag_len, unsigned char *tag)
 This function performs GCM encryption or decryption of a buffer.
 
int mbedtls_gcm_auth_decrypt (mbedtls_gcm_context *ctx, size_t length, const unsigned char *iv, size_t iv_len, const unsigned char *add, size_t add_len, const unsigned char *tag, size_t tag_len, const unsigned char *input, unsigned char *output)
 This function performs a GCM authenticated decryption of a buffer.
 
int mbedtls_gcm_starts (mbedtls_gcm_context *ctx, int mode, const unsigned char *iv, size_t iv_len, const unsigned char *add, size_t add_len)
 This function starts a GCM encryption or decryption operation.
 
int mbedtls_gcm_update (mbedtls_gcm_context *ctx, size_t length, const unsigned char *input, unsigned char *output)
 This function feeds an input buffer into an ongoing GCM encryption or decryption operation.
 
int mbedtls_gcm_finish (mbedtls_gcm_context *ctx, unsigned char *tag, size_t tag_len)
 This function finishes the GCM operation and generates the authentication tag.
 
void mbedtls_gcm_free (mbedtls_gcm_context *ctx)
 This function clears a GCM context and the underlying cipher sub-context.
 

Macro Definition Documentation

#define MBEDTLS_ERR_GCM_AUTH_FAILED   -0x0012

Authenticated decryption failed.

Definition at line 71 of file gcm_alt.h.

#define MBEDTLS_ERR_GCM_BAD_INPUT   -0x0014

Bad input parameters to function.

Definition at line 73 of file gcm_alt.h.

#define MBEDTLS_ERR_GCM_HW_ACCEL_FAILED   -0x0013

GCM hardware accelerator failed.

Definition at line 72 of file gcm_alt.h.

#define MBEDTLS_GCM_DECRYPT   0

Definition at line 69 of file gcm_alt.h.

#define MBEDTLS_GCM_ENCRYPT   1

Definition at line 68 of file gcm_alt.h.

Function Documentation

int mbedtls_gcm_auth_decrypt ( mbedtls_gcm_context *  ctx,
size_t  length,
const unsigned char *  iv,
size_t  iv_len,
const unsigned char *  add,
size_t  add_len,
const unsigned char *  tag,
size_t  tag_len,
const unsigned char *  input,
unsigned char *  output 
)

This function performs a GCM authenticated decryption of a buffer.

Note
For decryption, the output buffer cannot be the same as input buffer. If the buffers overlap, the output buffer must trail at least 8 Bytes behind the input buffer.
Parameters
ctxThe GCM context.
lengthThe length of the ciphertext to decrypt, which is also the length of the decrypted plaintext.
ivThe initialization vector.
iv_lenThe length of the IV.
addThe buffer holding the additional data.
add_lenThe length of the additional data.
tagThe buffer holding the tag to verify.
tag_lenThe length of the tag to verify.
inputThe buffer holding the ciphertext. Its size is length.
outputThe buffer for holding the decrypted plaintext. It must have room for length bytes.
Returns
0 if successful and authenticated.
MBEDTLS_ERR_GCM_AUTH_FAILED if the tag does not match.
MBEDTLS_ERR_GCM_BAD_INPUT if the lengths are not valid.
MBEDTLS_ERR_GCM_HW_ACCEL_FAILED or a cipher-specific error code if the decryption failed.
int mbedtls_gcm_crypt_and_tag ( mbedtls_gcm_context *  ctx,
int  mode,
size_t  length,
const unsigned char *  iv,
size_t  iv_len,
const unsigned char *  add,
size_t  add_len,
const unsigned char *  input,
unsigned char *  output,
size_t  tag_len,
unsigned char *  tag 
)

This function performs GCM encryption or decryption of a buffer.

Note
For encryption, the output buffer can be the same as the input buffer. For decryption, the output buffer cannot be the same as input buffer. If the buffers overlap, the output buffer must trail at least 8 Bytes behind the input buffer.
Warning
When this function performs a decryption, it outputs the authentication tag and does not verify that the data is authentic. You should use this function to perform encryption only. For decryption, use mbedtls_gcm_auth_decrypt() instead.
Parameters
ctxThe GCM context to use for encryption or decryption.
modeThe operation to perform:
  • MBEDTLS_GCM_ENCRYPT to perform authenticated encryption. The ciphertext is written to output and the authentication tag is written to tag.
  • MBEDTLS_GCM_DECRYPT to perform decryption. The plaintext is written to output and the authentication tag is written to tag. Note that this mode is not recommended, because it does not verify the authenticity of the data. For this reason, you should use mbedtls_gcm_auth_decrypt() instead of calling this function in decryption mode.
lengthThe length of the input data, which is equal to the length of the output data.
ivThe initialization vector.
iv_lenThe length of the IV.
addThe buffer holding the additional data.
add_lenThe length of the additional data.
inputThe buffer holding the input data. Its size is length.
outputThe buffer for holding the output data. It must have room for length bytes.
tag_lenThe length of the tag to generate.
tagThe buffer for holding the tag.
Returns
0 if the encryption or decryption was performed successfully. Note that in MBEDTLS_GCM_DECRYPT mode, this does not indicate that the data is authentic.
MBEDTLS_ERR_GCM_BAD_INPUT if the lengths are not valid.
MBEDTLS_ERR_GCM_HW_ACCEL_FAILED or a cipher-specific error code if the encryption or decryption failed.
int mbedtls_gcm_finish ( mbedtls_gcm_context *  ctx,
unsigned char *  tag,
size_t  tag_len 
)

This function finishes the GCM operation and generates the authentication tag.

It wraps up the GCM stream, and generates the tag. The tag can have a maximum length of 16 Bytes.

Parameters
ctxThe GCM context.
tagThe buffer for holding the tag.
tag_lenThe length of the tag to generate. Must be at least four.
Returns
0 on success, or MBEDTLS_ERR_GCM_BAD_INPUT on failure.
void mbedtls_gcm_free ( mbedtls_gcm_context *  ctx)

This function clears a GCM context and the underlying cipher sub-context.

Parameters
ctxThe GCM context to clear.
void mbedtls_gcm_init ( mbedtls_gcm_context *  ctx)

This function initializes the specified GCM context, to make references valid, and prepares the context for mbedtls_gcm_setkey() or mbedtls_gcm_free().

The function does not bind the GCM context to a particular cipher, nor set the key. For this purpose, use mbedtls_gcm_setkey().

Parameters
ctxThe GCM context to initialize.
int mbedtls_gcm_setkey ( mbedtls_gcm_context *  ctx,
mbedtls_cipher_id_t  cipher,
const unsigned char *  key,
unsigned int  keybits 
)

This function associates a GCM context with a cipher algorithm and a key.

Parameters
ctxThe GCM context to initialize.
cipherThe 128-bit block cipher to use.
keyThe encryption key.
keybitsThe key size in bits. Valid options are:
  • 128 bits
  • 192 bits
  • 256 bits
Returns
0 on success, or a cipher specific error code.
int mbedtls_gcm_starts ( mbedtls_gcm_context *  ctx,
int  mode,
const unsigned char *  iv,
size_t  iv_len,
const unsigned char *  add,
size_t  add_len 
)

This function starts a GCM encryption or decryption operation.

Parameters
ctxThe GCM context.
modeThe operation to perform: MBEDTLS_GCM_ENCRYPT or MBEDTLS_GCM_DECRYPT.
ivThe initialization vector.
iv_lenThe length of the IV.
addThe buffer holding the additional data, or NULL if add_len is 0.
add_lenThe length of the additional data. If 0, add is NULL.
Returns
0 on success.
int mbedtls_gcm_update ( mbedtls_gcm_context *  ctx,
size_t  length,
const unsigned char *  input,
unsigned char *  output 
)

This function feeds an input buffer into an ongoing GCM encryption or decryption operation.

` The function expects input to be a multiple of 16 Bytes. Only the last call before calling mbedtls_gcm_finish() can be less than 16 Bytes.

Note
For decryption, the output buffer cannot be the same as input buffer. If the buffers overlap, the output buffer must trail at least 8 Bytes behind the input buffer.
Parameters
ctxThe GCM context.
lengthThe length of the input data. This must be a multiple of 16 except in the last call before mbedtls_gcm_finish().
inputThe buffer holding the input data.
outputThe buffer for holding the output data.
Returns
0 on success, or MBEDTLS_ERR_GCM_BAD_INPUT on failure.