Loading...
Searching...
No Matches
Asn1_module

## Data Structures

struct | mbedtls_asn1_buf
struct | mbedtls_asn1_bitstring
struct | mbedtls_asn1_sequence
struct | mbedtls_asn1_named_data

## Macros

#define | MBEDTLS_OID_SIZE(x) (sizeof(x) - 1)
#define | MBEDTLS_OID_CMP(oid_str, oid_buf)
#define | MBEDTLS_OID_CMP_RAW(oid_str, oid_buf, oid_buf_len)

## Functions to parse ASN.1 data structures

typedef struct mbedtls_asn1_buf | mbedtls_asn1_buf
typedef struct mbedtls_asn1_bitstring | mbedtls_asn1_bitstring
typedef struct mbedtls_asn1_sequence | mbedtls_asn1_sequence
typedef struct mbedtls_asn1_named_data | mbedtls_asn1_named_data
int | mbedtls_asn1_get_len (unsigned char **p, const unsigned char *end, size_t *len)
| Get the length of an ASN.1 element. Updates the pointer to immediately behind the length.
int | mbedtls_asn1_get_tag (unsigned char **p, const unsigned char *end, size_t *len, int tag)
| Get the tag and length of the element. Check for the requested tag. Updates the pointer to immediately behind the tag and length.
int | mbedtls_asn1_get_bool (unsigned char **p, const unsigned char *end, int *val)
| Retrieve a boolean ASN.1 tag and its value. Updates the pointer to immediately behind the full tag.
int | mbedtls_asn1_get_int (unsigned char **p, const unsigned char *end, int *val)
| Retrieve an integer ASN.1 tag and its value. Updates the pointer to immediately behind the full tag.
int | mbedtls_asn1_get_enum (unsigned char **p, const unsigned char *end, int *val)
| Retrieve an enumerated ASN.1 tag and its value. Updates the pointer to immediately behind the full tag.
int | mbedtls_asn1_get_bitstring (unsigned char **p, const unsigned char *end, mbedtls_asn1_bitstring *bs)
| Retrieve a bitstring ASN.1 tag and its value. Updates the pointer to immediately behind the full tag.
int | mbedtls_asn1_get_bitstring_null (unsigned char **p, const unsigned char *end, size_t *len)
| Retrieve a bitstring ASN.1 tag without unused bits and its value. Updates the pointer to the beginning of the bit/octet string.
int | mbedtls_asn1_get_sequence_of (unsigned char **p, const unsigned char *end, mbedtls_asn1_sequence *cur, int tag)
| Parses and splits an ASN.1 "SEQUENCE OF <tag>". Updates the pointer to immediately behind the full sequence tag.
void | mbedtls_asn1_sequence_free (mbedtls_asn1_sequence *seq)
| Free a heap-allocated linked list presentation of an ASN.1 sequence, including the first element.
int | mbedtls_asn1_traverse_sequence_of (unsigned char **p, const unsigned char *end, unsigned char tag_must_mask, unsigned char tag_must_val, unsigned char tag_may_mask, unsigned char tag_may_val, int(*cb)(void *ctx, int tag, unsigned char *start, size_t len), void *ctx)
| Traverse an ASN.1 SEQUENCE container and call a callback for each entry.
int | mbedtls_asn1_get_mpi (unsigned char **p, const unsigned char *end, mbedtls_mpi *X)
| Retrieve an integer ASN.1 tag and its value. Updates the pointer to immediately behind the full tag.
int | mbedtls_asn1_get_alg (unsigned char **p, const unsigned char *end, mbedtls_asn1_buf *alg, mbedtls_asn1_buf *params)
| Retrieve an AlgorithmIdentifier ASN.1 sequence. Updates the pointer to immediately behind the full AlgorithmIdentifier.
int | mbedtls_asn1_get_alg_null (unsigned char **p, const unsigned char *end, mbedtls_asn1_buf *alg)
| Retrieve an AlgorithmIdentifier ASN.1 sequence with NULL or no params. Updates the pointer to immediately behind the full AlgorithmIdentifier.
mbedtls_asn1_named_data * | mbedtls_asn1_find_named_data (mbedtls_asn1_named_data *list, const char *oid, size_t len)
| Find a specific named_data entry in a sequence or list based on the OID.
void | mbedtls_asn1_free_named_data (mbedtls_asn1_named_data *entry)
| Free a mbedtls_asn1_named_data entry.
void | mbedtls_asn1_free_named_data_list (mbedtls_asn1_named_data **head)
| Free all entries in a mbedtls_asn1_named_data list.

## ASN1 Error codes

These error codes are OR'ed to X509 error codes for higher error granularity. ASN1 is a standard to specify data structures.
#define | MBEDTLS_ERR_ASN1_OUT_OF_DATA -0x0060
#define | MBEDTLS_ERR_ASN1_UNEXPECTED_TAG -0x0062
#define | MBEDTLS_ERR_ASN1_INVALID_LENGTH -0x0064
#define | MBEDTLS_ERR_ASN1_LENGTH_MISMATCH -0x0066
#define | MBEDTLS_ERR_ASN1_INVALID_DATA -0x0068
#define | MBEDTLS_ERR_ASN1_ALLOC_FAILED -0x006A
#define | MBEDTLS_ERR_ASN1_BUF_TOO_SMALL -0x006C

## DER constants

These constants comply with the DER encoded ASN.1 type tags. DER encoding uses hexadecimal representation. An example DER sequence is:

- 0x02 – tag indicating INTEGER
- 0x01 – length in octets
- 0x05 – value Such sequences are typically read into `mbedtls_x509_buf`.

#define | MBEDTLS_ASN1_BOOLEAN 0x01
#define | MBEDTLS_ASN1_INTEGER 0x02
#define | MBEDTLS_ASN1_BIT_STRING 0x03
#define | MBEDTLS_ASN1_OCTET_STRING 0x04
#define | MBEDTLS_ASN1_NULL 0x05
#define | MBEDTLS_ASN1_OID 0x06
#define | MBEDTLS_ASN1_ENUMERATED 0x0A
#define | MBEDTLS_ASN1_UTF8_STRING 0x0C
#define | MBEDTLS_ASN1_SEQUENCE 0x10
#define | MBEDTLS_ASN1_SET 0x11
#define | MBEDTLS_ASN1_PRINTABLE_STRING 0x13
#define | MBEDTLS_ASN1_T61_STRING 0x14
#define | MBEDTLS_ASN1_IA5_STRING 0x16
#define | MBEDTLS_ASN1_UTC_TIME 0x17
#define | MBEDTLS_ASN1_GENERALIZED_TIME 0x18
#define | MBEDTLS_ASN1_UNIVERSAL_STRING 0x1C
#define | MBEDTLS_ASN1_BMP_STRING 0x1E
#define | MBEDTLS_ASN1_PRIMITIVE 0x00
#define | MBEDTLS_ASN1_CONSTRUCTED 0x20
#define | MBEDTLS_ASN1_CONTEXT_SPECIFIC 0x80
#define | MBEDTLS_ASN1_IS_STRING_TAG(tag)
#define | MBEDTLS_ASN1_TAG_CLASS_MASK 0xC0
#define | MBEDTLS_ASN1_TAG_PC_MASK 0x20
#define | MBEDTLS_ASN1_TAG_VALUE_MASK 0x1F

## Detailed Description

## Macro Definition Documentation

## MBEDTLS_ASN1_BIT_STRING

#define MBEDTLS_ASN1_BIT_STRING 0x03

Definition at line 67 of file asn1.h.

## MBEDTLS_ASN1_BMP_STRING

#define MBEDTLS_ASN1_BMP_STRING 0x1E

Definition at line 81 of file asn1.h.

## MBEDTLS_ASN1_BOOLEAN

#define MBEDTLS_ASN1_BOOLEAN 0x01

Definition at line 65 of file asn1.h.

## MBEDTLS_ASN1_CONSTRUCTED

#define MBEDTLS_ASN1_CONSTRUCTED 0x20

Definition at line 83 of file asn1.h.

## MBEDTLS_ASN1_CONTEXT_SPECIFIC

#define MBEDTLS_ASN1_CONTEXT_SPECIFIC 0x80

Definition at line 84 of file asn1.h.

## MBEDTLS_ASN1_ENUMERATED

#define MBEDTLS_ASN1_ENUMERATED 0x0A

Definition at line 71 of file asn1.h.

## MBEDTLS_ASN1_GENERALIZED_TIME

#define MBEDTLS_ASN1_GENERALIZED_TIME 0x18

Definition at line 79 of file asn1.h.

## MBEDTLS_ASN1_IA5_STRING

#define MBEDTLS_ASN1_IA5_STRING 0x16

Definition at line 77 of file asn1.h.

## MBEDTLS_ASN1_INTEGER

#define MBEDTLS_ASN1_INTEGER 0x02

Definition at line 66 of file asn1.h.

## MBEDTLS_ASN1_IS_STRING_TAG

#define MBEDTLS_ASN1_IS_STRING_TAG | ( |  | tag | ) |

Value:
((tag) < 32u && ( \
((1u << (tag)) & ((1u << MBEDTLS_ASN1_BMP_STRING) | \
(1u << MBEDTLS_ASN1_UTF8_STRING) | \
(1u << MBEDTLS_ASN1_T61_STRING) | \
(1u << MBEDTLS_ASN1_IA5_STRING) | \
(1u << MBEDTLS_ASN1_UNIVERSAL_STRING) | \
(1u << MBEDTLS_ASN1_PRINTABLE_STRING) | \
(1u << MBEDTLS_ASN1_BIT_STRING))) != 0))
MBEDTLS_ASN1_IA5_STRING
#define MBEDTLS_ASN1_IA5_STRING
Definition asn1.h:77
MBEDTLS_ASN1_BMP_STRING
#define MBEDTLS_ASN1_BMP_STRING
Definition asn1.h:81
MBEDTLS_ASN1_PRINTABLE_STRING
#define MBEDTLS_ASN1_PRINTABLE_STRING
Definition asn1.h:75
MBEDTLS_ASN1_T61_STRING
#define MBEDTLS_ASN1_T61_STRING
Definition asn1.h:76
MBEDTLS_ASN1_UNIVERSAL_STRING
#define MBEDTLS_ASN1_UNIVERSAL_STRING
Definition asn1.h:80
MBEDTLS_ASN1_UTF8_STRING
#define MBEDTLS_ASN1_UTF8_STRING
Definition asn1.h:72
MBEDTLS_ASN1_BIT_STRING
#define MBEDTLS_ASN1_BIT_STRING
Definition asn1.h:67

Definition at line 88 of file asn1.h.

## MBEDTLS_ASN1_NULL

#define MBEDTLS_ASN1_NULL 0x05

Definition at line 69 of file asn1.h.

## MBEDTLS_ASN1_OCTET_STRING

#define MBEDTLS_ASN1_OCTET_STRING 0x04

Definition at line 68 of file asn1.h.

## MBEDTLS_ASN1_OID

#define MBEDTLS_ASN1_OID 0x06

Definition at line 70 of file asn1.h.

## MBEDTLS_ASN1_PRIMITIVE

#define MBEDTLS_ASN1_PRIMITIVE 0x00

Definition at line 82 of file asn1.h.

## MBEDTLS_ASN1_PRINTABLE_STRING

#define MBEDTLS_ASN1_PRINTABLE_STRING 0x13

Definition at line 75 of file asn1.h.

## MBEDTLS_ASN1_SEQUENCE

#define MBEDTLS_ASN1_SEQUENCE 0x10

Definition at line 73 of file asn1.h.

## MBEDTLS_ASN1_SET

#define MBEDTLS_ASN1_SET 0x11

Definition at line 74 of file asn1.h.

## MBEDTLS_ASN1_T61_STRING

#define MBEDTLS_ASN1_T61_STRING 0x14

Definition at line 76 of file asn1.h.

## MBEDTLS_ASN1_TAG_CLASS_MASK

#define MBEDTLS_ASN1_TAG_CLASS_MASK 0xC0

Definition at line 108 of file asn1.h.

## MBEDTLS_ASN1_TAG_PC_MASK

#define MBEDTLS_ASN1_TAG_PC_MASK 0x20

Definition at line 109 of file asn1.h.

## MBEDTLS_ASN1_TAG_VALUE_MASK

#define MBEDTLS_ASN1_TAG_VALUE_MASK 0x1F

Definition at line 110 of file asn1.h.

## MBEDTLS_ASN1_UNIVERSAL_STRING

#define MBEDTLS_ASN1_UNIVERSAL_STRING 0x1C

Definition at line 80 of file asn1.h.

## MBEDTLS_ASN1_UTC_TIME

#define MBEDTLS_ASN1_UTC_TIME 0x17

Definition at line 78 of file asn1.h.

## MBEDTLS_ASN1_UTF8_STRING

#define MBEDTLS_ASN1_UTF8_STRING 0x0C

Definition at line 72 of file asn1.h.

## MBEDTLS_ERR_ASN1_ALLOC_FAILED

#define MBEDTLS_ERR_ASN1_ALLOC_FAILED -0x006A

Memory allocation failed

Definition at line 48 of file asn1.h.

## MBEDTLS_ERR_ASN1_BUF_TOO_SMALL

#define MBEDTLS_ERR_ASN1_BUF_TOO_SMALL -0x006C

Buffer too small when writing ASN.1 data structure.

Definition at line 50 of file asn1.h.

## MBEDTLS_ERR_ASN1_INVALID_DATA

#define MBEDTLS_ERR_ASN1_INVALID_DATA -0x0068

Data is invalid.

Definition at line 46 of file asn1.h.

## MBEDTLS_ERR_ASN1_INVALID_LENGTH

#define MBEDTLS_ERR_ASN1_INVALID_LENGTH -0x0064

Error when trying to determine the length or invalid length.

Definition at line 42 of file asn1.h.

## MBEDTLS_ERR_ASN1_LENGTH_MISMATCH

#define MBEDTLS_ERR_ASN1_LENGTH_MISMATCH -0x0066

Actual length differs from expected length.

Definition at line 44 of file asn1.h.

## MBEDTLS_ERR_ASN1_OUT_OF_DATA

#define MBEDTLS_ERR_ASN1_OUT_OF_DATA -0x0060

Out of data when parsing an ASN1 data structure.

Definition at line 38 of file asn1.h.

## MBEDTLS_ERR_ASN1_UNEXPECTED_TAG

#define MBEDTLS_ERR_ASN1_UNEXPECTED_TAG -0x0062

ASN1 tag was of an unexpected value.

Definition at line 40 of file asn1.h.

## MBEDTLS_OID_CMP

#define MBEDTLS_OID_CMP | ( |  | oid_str,
|  |  | oid_buf
| ) |  |

Value:
((MBEDTLS_OID_SIZE(oid_str) != (oid_buf)->len) || \
memcmp((oid_str), (oid_buf)->p, (oid_buf)->len) != 0)
MBEDTLS_OID_SIZE
#define MBEDTLS_OID_SIZE(x)
Definition asn1.h:115

Compares an mbedtls_asn1_buf structure to a reference OID.

Only works for 'defined' oid_str values (MBEDTLS_OID_HMAC_SHA1), you cannot use a 'unsigned char *oid' here!

Definition at line 123 of file asn1.h.

## MBEDTLS_OID_CMP_RAW

#define MBEDTLS_OID_CMP_RAW | ( |  | oid_str,
|  |  | oid_buf,
|  |  | oid_buf_len
| ) |  |

Value:
((MBEDTLS_OID_SIZE(oid_str) != (oid_buf_len)) || \
memcmp((oid_str), (oid_buf), (oid_buf_len)) != 0)

Definition at line 127 of file asn1.h.

## MBEDTLS_OID_SIZE

#define MBEDTLS_OID_SIZE | ( |  | x | ) | (sizeof(x) - 1)

Returns the size of the binary string, without the trailing \0

Definition at line 115 of file asn1.h.

## Typedef Documentation

## mbedtls_asn1_bitstring

typedef struct mbedtls_asn1_bitstring mbedtls_asn1_bitstring

Container for ASN1 bit strings.

## mbedtls_asn1_buf

typedef struct mbedtls_asn1_buf mbedtls_asn1_buf

Type-length-value structure that allows for ASN1 using DER.

## mbedtls_asn1_named_data

typedef struct mbedtls_asn1_named_data mbedtls_asn1_named_data

Container for a sequence or list of 'named' ASN.1 data items

## mbedtls_asn1_sequence

typedef struct mbedtls_asn1_sequence mbedtls_asn1_sequence

Container for a sequence of ASN.1 items

## Function Documentation

## mbedtls_asn1_find_named_data()

mbedtls_asn1_named_data * mbedtls_asn1_find_named_data | ( | mbedtls_asn1_named_data * | list,
|  | const char * | oid,
|  | size_t | len
| ) |  |

Find a specific named_data entry in a sequence or list based on the OID.

Parameters

  list | The list to seek through
  oid | The OID to look for
  len | Size of the OID

Returns
  NULL if not found, or a pointer to the existing entry.

## mbedtls_asn1_free_named_data()

void mbedtls_asn1_free_named_data | ( | mbedtls_asn1_named_data * | entry | ) |

Free a mbedtls_asn1_named_data entry.

Parameters

  entry | The named data entry to free. This function calls mbedtls_free() on `entry->oid.p` and `entry->val.p`.

## mbedtls_asn1_free_named_data_list()

void mbedtls_asn1_free_named_data_list | ( | mbedtls_asn1_named_data ** | head | ) |

Free all entries in a mbedtls_asn1_named_data list.

Parameters

  head | Pointer to the head of the list of named data entries to free. This function calls mbedtls_asn1_free_named_data() and mbedtls_free() on each list element and sets `*head` to `NULL`.

## mbedtls_asn1_get_alg()

int mbedtls_asn1_get_alg | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | mbedtls_asn1_buf * | alg,
|  | mbedtls_asn1_buf * | params
| ) |  |

Retrieve an AlgorithmIdentifier ASN.1 sequence. Updates the pointer to immediately behind the full AlgorithmIdentifier.

Parameters

  p | On entry, `*p` points to the start of the ASN.1 element. On successful completion, `*p` points to the first byte beyond the AlgorithmIdentifier element. On error, the value of `*p` is undefined.
  end | End of data.
  alg | The buffer to receive the OID.
  params | The buffer to receive the parameters. This is zeroized if there are no parameters.

Returns
  0 if successful or a specific ASN.1 or MPI error code.

## mbedtls_asn1_get_alg_null()

int mbedtls_asn1_get_alg_null | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | mbedtls_asn1_buf * | alg
| ) |  |

Retrieve an AlgorithmIdentifier ASN.1 sequence with NULL or no params. Updates the pointer to immediately behind the full AlgorithmIdentifier.

Parameters

  p | On entry, `*p` points to the start of the ASN.1 element. On successful completion, `*p` points to the first byte beyond the AlgorithmIdentifier element. On error, the value of `*p` is undefined.
  end | End of data.
  alg | The buffer to receive the OID.

Returns
  0 if successful or a specific ASN.1 or MPI error code.

## mbedtls_asn1_get_bitstring()

int mbedtls_asn1_get_bitstring | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | mbedtls_asn1_bitstring * | bs
| ) |  |

Retrieve a bitstring ASN.1 tag and its value. Updates the pointer to immediately behind the full tag.

Parameters

  p | On entry, `*p` points to the start of the ASN.1 element. On successful completion, `*p` is equal to `end`. On error, the value of `*p` is undefined.
  end | End of data.
  bs | On success, mbedtls_asn1_bitstring information about the parsed value.

Returns
  0 if successful.
  MBEDTLS_ERR_ASN1_LENGTH_MISMATCH if the input contains extra data after a valid BIT STRING.
  An ASN.1 error code if the input does not start with a valid ASN.1 BIT STRING.

## mbedtls_asn1_get_bitstring_null()

int mbedtls_asn1_get_bitstring_null | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | size_t * | len
| ) |  |

Retrieve a bitstring ASN.1 tag without unused bits and its value. Updates the pointer to the beginning of the bit/octet string.

Parameters

  p | On entry, `*p` points to the start of the ASN.1 element. On successful completion, `*p` points to the first byte of the content of the BIT STRING. On error, the value of `*p` is undefined.
  end | End of data.
  len | On success, `*len` is the length of the content in bytes.

Returns
  0 if successful.
  MBEDTLS_ERR_ASN1_INVALID_DATA if the input starts with a valid BIT STRING with a nonzero number of unused bits.
  An ASN.1 error code if the input does not start with a valid ASN.1 BIT STRING.

## mbedtls_asn1_get_bool()

int mbedtls_asn1_get_bool | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | int * | val
| ) |  |

Retrieve a boolean ASN.1 tag and its value. Updates the pointer to immediately behind the full tag.

Parameters

  p | On entry, `*p` points to the start of the ASN.1 element. On successful completion, `*p` points to the first byte beyond the ASN.1 element. On error, the value of `*p` is undefined.
  end | End of data.
  val | On success, the parsed value (`0` or `1`).

Returns
  0 if successful.
  An ASN.1 error code if the input does not start with a valid ASN.1 BOOLEAN.

## mbedtls_asn1_get_enum()

int mbedtls_asn1_get_enum | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | int * | val
| ) |  |

Retrieve an enumerated ASN.1 tag and its value. Updates the pointer to immediately behind the full tag.

Parameters

  p | On entry, `*p` points to the start of the ASN.1 element. On successful completion, `*p` points to the first byte beyond the ASN.1 element. On error, the value of `*p` is undefined.
  end | End of data.
  val | On success, the parsed value.

Returns
  0 if successful.
  An ASN.1 error code if the input does not start with a valid ASN.1 ENUMERATED.
  MBEDTLS_ERR_ASN1_INVALID_LENGTH if the parsed value does not fit in an `int`.

## mbedtls_asn1_get_int()

int mbedtls_asn1_get_int | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | int * | val
| ) |  |

Retrieve an integer ASN.1 tag and its value. Updates the pointer to immediately behind the full tag.

Parameters

  p | On entry, `*p` points to the start of the ASN.1 element. On successful completion, `*p` points to the first byte beyond the ASN.1 element. On error, the value of `*p` is undefined.
  end | End of data.
  val | On success, the parsed value.

Returns
  0 if successful.
  An ASN.1 error code if the input does not start with a valid ASN.1 INTEGER.
  MBEDTLS_ERR_ASN1_INVALID_LENGTH if the parsed value does not fit in an `int`.

## mbedtls_asn1_get_len()

int mbedtls_asn1_get_len | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | size_t * | len
| ) |  |

Get the length of an ASN.1 element. Updates the pointer to immediately behind the length.

Parameters

  p | On entry, `*p` points to the first byte of the length, i.e. immediately after the tag. On successful completion, `*p` points to the first byte after the length, i.e. the first byte of the content. On error, the value of `*p` is undefined.
  end | End of data.
  len | On successful completion, `*len` contains the length read from the ASN.1 input.

Returns
  0 if successful.
  MBEDTLS_ERR_ASN1_OUT_OF_DATA if the ASN.1 element would end beyond `end`.
  MBEDTLS_ERR_ASN1_INVALID_LENGTH if the length is unparsable.

## mbedtls_asn1_get_mpi()

int mbedtls_asn1_get_mpi | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | mbedtls_mpi * | X
| ) |  |

Retrieve an integer ASN.1 tag and its value. Updates the pointer to immediately behind the full tag.

Parameters

  p | On entry, `*p` points to the start of the ASN.1 element. On successful completion, `*p` points to the first byte beyond the ASN.1 element. On error, the value of `*p` is undefined.
  end | End of data.
  X | On success, the parsed value.

Returns
  0 if successful.
  An ASN.1 error code if the input does not start with a valid ASN.1 INTEGER.
  MBEDTLS_ERR_ASN1_INVALID_LENGTH if the parsed value does not fit in an `int`.
  An MPI error code if the parsed value is too large.

## mbedtls_asn1_get_sequence_of()

int mbedtls_asn1_get_sequence_of | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | mbedtls_asn1_sequence * | cur,
|  | int | tag
| ) |  |

Parses and splits an ASN.1 "SEQUENCE OF <tag>". Updates the pointer to immediately behind the full sequence tag.

This function allocates memory for the sequence elements. You can free the allocated memory with mbedtls_asn1_sequence_free().

Note
  On error, this function may return a partial list in `cur`. You must set `cur->next = NULL` before calling this function! Otherwise it is impossible to distinguish a previously non-null pointer from a pointer to an object allocated by this function.
  If the sequence is empty, this function does not modify `*cur`. If the sequence is valid and non-empty, this function sets `cur->buf.tag` to `tag`. This allows callers to distinguish between an empty sequence and a one-element sequence.

Parameters

  p | On entry, `*p` points to the start of the ASN.1 element. On successful completion, `*p` is equal to `end`. On error, the value of `*p` is undefined.
  end | End of data.

  cur

  A mbedtls_asn1_sequence which this function fills. When this function returns, `*cur` is the head of a linked list. Each node in this list is allocated with mbedtls_calloc() apart from `cur` itself, and should therefore be freed with mbedtls_free(). The list describes the content of the sequence. The head of the list (i.e. `*cur` itself) describes the first element, `*cur->next` describes the second element, etc. For each element, `buf.tag == tag`, `buf.len` is the length of the content of the content of the element, and `buf.p` points to the first byte of the content (i.e. immediately past the length of the element). Note that list elements may be allocated even on error.

  tag | Each element of the sequence must have this tag.

Returns
  0 if successful.
  MBEDTLS_ERR_ASN1_LENGTH_MISMATCH if the input contains extra data after a valid SEQUENCE OF `tag`.
  MBEDTLS_ERR_ASN1_UNEXPECTED_TAG if the input starts with an ASN.1 SEQUENCE in which an element has a tag that is different from `tag`.
  MBEDTLS_ERR_ASN1_ALLOC_FAILED if a memory allocation failed.
  An ASN.1 error code if the input does not start with a valid ASN.1 SEQUENCE.

## mbedtls_asn1_get_tag()

int mbedtls_asn1_get_tag | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | size_t * | len,
|  | int | tag
| ) |  |

Get the tag and length of the element. Check for the requested tag. Updates the pointer to immediately behind the tag and length.

Parameters

  p | On entry, `*p` points to the start of the ASN.1 element. On successful completion, `*p` points to the first byte after the length, i.e. the first byte of the content. On error, the value of `*p` is undefined.
  end | End of data.
  len | On successful completion, `*len` contains the length read from the ASN.1 input.
  tag | The expected tag.

Returns
  0 if successful.
  MBEDTLS_ERR_ASN1_UNEXPECTED_TAG if the data does not start with the requested tag.
  MBEDTLS_ERR_ASN1_OUT_OF_DATA if the ASN.1 element would end beyond `end`.
  MBEDTLS_ERR_ASN1_INVALID_LENGTH if the length is unparsable.

## mbedtls_asn1_sequence_free()

void mbedtls_asn1_sequence_free | ( | mbedtls_asn1_sequence * | seq | ) |

Free a heap-allocated linked list presentation of an ASN.1 sequence, including the first element.

There are two common ways to manage the memory used for the representation of a parsed ASN.1 sequence:

- Allocate a head node `mbedtls_asn1_sequence *head` with mbedtls_calloc(). Pass this node as the `cur` argument to mbedtls_asn1_get_sequence_of(). When you have finished processing the sequence, call mbedtls_asn1_sequence_free() on `head`.
- Allocate a head node `mbedtls_asn1_sequence *head` in any manner, for example on the stack. Make sure that `head->next == NULL`. Pass `head` as the `cur` argument to mbedtls_asn1_get_sequence_of(). When you have finished processing the sequence, call mbedtls_asn1_sequence_free() on `head->cur`, then free `head` itself in the appropriate manner.

Parameters

  seq | The address of the first sequence component. This may be `NULL`, in which case this functions returns immediately.

## mbedtls_asn1_traverse_sequence_of()

int mbedtls_asn1_traverse_sequence_of | ( | unsigned char ** | p,
|  | const unsigned char * | end,
|  | unsigned char | tag_must_mask,
|  | unsigned char | tag_must_val,
|  | unsigned char | tag_may_mask,
|  | unsigned char | tag_may_val,
|  | int(*)(void *ctx, int tag, unsigned char *start, size_t len) | cb,
|  | void * | ctx
| ) |  |

Traverse an ASN.1 SEQUENCE container and call a callback for each entry.

This function checks that the input is a SEQUENCE of elements that each have a "must" tag, and calls a callback function on the elements that have a "may" tag.

For example, to validate that the input is a SEQUENCE of `tag1` and call `cb` on each element, use

mbedtls_asn1_traverse_sequence_of(&p, end, 0xff, tag1, 0, 0, cb, ctx);
mbedtls_asn1_traverse_sequence_of
int mbedtls_asn1_traverse_sequence_of(unsigned char **p, const unsigned char *end, unsigned char tag_must_mask, unsigned char tag_must_val, unsigned char tag_may_mask, unsigned char tag_may_val, int(*cb)(void *ctx, int tag, unsigned char *start, size_t len), void *ctx)
Traverse an ASN.1 SEQUENCE container and call a callback for each entry.

To validate that the input is a SEQUENCE of ANY and call `cb` on each element, use

mbedtls_asn1_traverse_sequence_of(&p, end, 0, 0, 0, 0, cb, ctx);

To validate that the input is a SEQUENCE of CHOICE {NULL, OCTET STRING} and call `cb` on each element that is an OCTET STRING, use

mbedtls_asn1_traverse_sequence_of(&p, end, 0xfe, 0x04, 0xff, 0x04, cb, ctx);

The callback is called on the elements with a "may" tag from left to right. If the input is not a valid SEQUENCE of elements with a "must" tag, the callback is called on the elements up to the leftmost point where the input is invalid.

Warning
  This function is still experimental and may change at any time.

Parameters

  p | The address of the pointer to the beginning of the ASN.1 SEQUENCE header. This is updated to point to the end of the ASN.1 SEQUENCE container on a successful invocation.
  end | The end of the ASN.1 SEQUENCE container.
  tag_must_mask | A mask to be applied to the ASN.1 tags found within the SEQUENCE before comparing to `tag_must_val`.
  tag_must_val | The required value of each ASN.1 tag found in the SEQUENCE, after masking with `tag_must_mask`. Mismatching tags lead to an error. For example, a value of `0` for both `tag_must_mask` and `tag_must_val` means that every tag is allowed, while a value of `0xFF` for `tag_must_mask` means that `tag_must_val` is the only allowed tag.
  tag_may_mask | A mask to be applied to the ASN.1 tags found within the SEQUENCE before comparing to `tag_may_val`.
  tag_may_val | The desired value of each ASN.1 tag found in the SEQUENCE, after masking with `tag_may_mask`. Mismatching tags will be silently ignored. For example, a value of `0` for `tag_may_mask` and `tag_may_val` means that any tag will be considered, while a value of `0xFF` for `tag_may_mask` means that all tags with value different from `tag_may_val` will be ignored.

  cb

  The callback to trigger for each component in the ASN.1 SEQUENCE that matches `tag_may_val`. The callback function is called with the following parameters:
  - `ctx`.
  - The tag of the current element.
  - A pointer to the start of the current element's content inside the input.
  - The length of the content of the current element. If the callback returns a non-zero value, the function stops immediately, forwarding the callback's return value.

  ctx | The context to be passed to the callback `cb`.

Returns
  `0` if successful the entire ASN.1 SEQUENCE was traversed without parsing or callback errors.
  MBEDTLS_ERR_ASN1_LENGTH_MISMATCH if the input contains extra data after a valid SEQUENCE of elements with an accepted tag.
  MBEDTLS_ERR_ASN1_UNEXPECTED_TAG if the input starts with an ASN.1 SEQUENCE in which an element has a tag that is not accepted.
  An ASN.1 error code if the input does not start with a valid ASN.1 SEQUENCE.
  A non-zero error code forwarded from the callback `cb` in case the latter returns a non-zero value.