gcm.h File Reference

This file contains GCM definitions and functions. More...

`#include "config.h"`
`#include "cipher.h"`
`#include <stdint.h>`
Include dependency graph for gcm.h:

Go to the source code of this file.

## Data Structures

struct | mbedtls_gcm_context
| The GCM context structure. More...

## 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

## Typedefs

typedef struct mbedtls_gcm_context | mbedtls_gcm_context
| The GCM context structure. More...

## 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(). More...
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. More...
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. More...
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. More...
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. More...
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. More...
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. More...
void | mbedtls_gcm_free (mbedtls_gcm_context *ctx)
| This function clears a GCM context and the underlying cipher sub-context. More...
int | mbedtls_gcm_self_test (int verbose)
| The GCM checkup routine. More...

## Detailed Description

This file contains GCM definitions and functions.

The Galois/Counter Mode (GCM) for 128-bit block ciphers is 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.

Definition in file gcm.h.

## Macro Definition Documentation

## MBEDTLS_ERR_GCM_AUTH_FAILED

#define MBEDTLS_ERR_GCM_AUTH_FAILED -0x0012

Authenticated decryption failed.

Definition at line 49 of file gcm.h.

## MBEDTLS_ERR_GCM_BAD_INPUT

#define MBEDTLS_ERR_GCM_BAD_INPUT -0x0014

Bad input parameters to function.

Definition at line 54 of file gcm.h.

## MBEDTLS_ERR_GCM_HW_ACCEL_FAILED

#define MBEDTLS_ERR_GCM_HW_ACCEL_FAILED -0x0013

GCM hardware accelerator failed.

Definition at line 52 of file gcm.h.

## MBEDTLS_GCM_DECRYPT

#define MBEDTLS_GCM_DECRYPT 0

Definition at line 47 of file gcm.h.

## MBEDTLS_GCM_ENCRYPT

#define MBEDTLS_GCM_ENCRYPT 1

Definition at line 46 of file gcm.h.

## Typedef Documentation

## mbedtls_gcm_context

typedef struct mbedtls_gcm_context mbedtls_gcm_context

The GCM context structure.

## Function Documentation

## mbedtls_gcm_auth_decrypt()

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

  ctx | The GCM context. This must be initialized.
  length | The length of the ciphertext to decrypt, which is also the length of the decrypted plaintext.
  iv | The initialization vector. This must be a readable buffer of at least `iv_len` Bytes.
  iv_len | The length of the IV.
  add | The buffer holding the additional data. This must be of at least that size in Bytes.
  add_len | The length of the additional data.
  tag | The buffer holding the tag to verify. This must be a readable buffer of at least `tag_len` Bytes.
  tag_len | The length of the tag to verify.
  input | The buffer holding the ciphertext. If `length` is greater than zero, this must be a readable buffer of at least that size.
  output | The buffer for holding the decrypted plaintext. If `length` is greater than zero, this must be a writable buffer of at least that size.

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 or pointers are not valid or a cipher-specific error code if the decryption failed.

## mbedtls_gcm_crypt_and_tag()

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

  ctx | The GCM context to use for encryption or decryption. This must be initialized.

  mode

  The 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.

  length | The length of the input data, which is equal to the length of the output data.
  iv | The initialization vector. This must be a readable buffer of at least `iv_len` Bytes.
  iv_len | The length of the IV.
  add | The buffer holding the additional data. This must be of at least that size in Bytes.
  add_len | The length of the additional data.
  input | The buffer holding the input data. If `length` is greater than zero, this must be a readable buffer of at least that size in Bytes.
  output | The buffer for holding the output data. If `length` is greater than zero, this must be a writable buffer of at least that size in Bytes.
  tag_len | The length of the tag to generate.
  tag | The buffer for holding the tag. This must be a readable buffer of at least `tag_len` Bytes.

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 or pointers are not valid or a cipher-specific error code if the encryption or decryption failed.

## mbedtls_gcm_finish()

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

  ctx | The GCM context. This must be initialized.
  tag | The buffer for holding the tag. This must be a readable buffer of at least `tag_len` Bytes.
  tag_len | The length of the tag to generate. This must be at least four.

Returns
  `0` on success.
  MBEDTLS_ERR_GCM_BAD_INPUT on failure.

## mbedtls_gcm_free()

void mbedtls_gcm_free | ( | mbedtls_gcm_context * | ctx | ) |

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

Parameters

  ctx | The GCM context to clear. If this is `NULL`, the call has no effect. Otherwise, this must be initialized.

## mbedtls_gcm_init()

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

  ctx | The GCM context to initialize. This must not be `NULL`.

## mbedtls_gcm_self_test()

int mbedtls_gcm_self_test | ( | int | verbose | ) |

The GCM checkup routine.

Returns
  `0` on success.
  `1` on failure.

## mbedtls_gcm_setkey()

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

  ctx | The GCM context. This must be initialized.
  cipher | The 128-bit block cipher to use.
  key | The encryption key. This must be a readable buffer of at least `keybits` bits.

  keybits

  The key size in bits. Valid options are:
  - 128 bits
  - 192 bits
  - 256 bits

Returns
  `0` on success.
  A cipher-specific error code on failure.

## mbedtls_gcm_starts()

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

  ctx | The GCM context. This must be initialized.
  mode | The operation to perform: MBEDTLS_GCM_ENCRYPT or MBEDTLS_GCM_DECRYPT.
  iv | The initialization vector. This must be a readable buffer of at least `iv_len` Bytes.
  iv_len | The length of the IV.
  add | The buffer holding the additional data, or `NULL` if `add_len` is `0`.
  add_len | The length of the additional data. If `0`, `add` may be `NULL`.

Returns
  `0` on success.

## mbedtls_gcm_update()

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

  ctx | The GCM context. This must be initialized.
  length | The length of the input data. This must be a multiple of 16 except in the last call before mbedtls_gcm_finish().
  input | The buffer holding the input data. If `length` is greater than zero, this must be a readable buffer of at least that size in Bytes.
  output | The buffer for holding the output data. If `length` is greater than zero, this must be a writable buffer of at least that size in Bytes.

Returns
  `0` on success.
  MBEDTLS_ERR_GCM_BAD_INPUT on failure.