asn1.h

DER/ASN.1 implementation \par License: GNU GPL v3.0 \par Reference: ITU-T X.690 (DER Encoding Rules)

Author: Anthony Cagliano

Enums

enum tls_asn1_tags

Values:

enumerator ASN1_RESVD: RESERVED.

enumerator ASN1_BOOLEAN: defines a BOOLEAN object

enumerator ASN1_INTEGER: defines an INTEGER object

enumerator ASN1_BITSTRING: defines a BIT STRING object

enumerator ASN1_OCTETSTRING: defines an OCTET STRING object

enumerator ASN1_NULL: defines a NULL object (0 size, no data)

enumerator ASN1_OBJECTID: defines an OBJECT IDENTIFIER

enumerator ASN1_OBJECTDESC: defines an OBJECT DESCRIPTION

enumerator ASN1_INSTANCE: defines an INSTANCE

enumerator ASN1_REAL: defines a REAL object

enumerator ASN1_ENUMERATED

enumerator ASN1_EMBEDDEDPDV

enumerator ASN1_UTF8STRING

enumerator ASN1_RELATIVEOID

enumerator ASN1_SEQUENCE: defines a SEQUENCE

enumerator ASN1_SET: defines a SET

enumerator ASN1_NUMERICSTRING

enumerator ASN1_PRINTABLESTRING

enumerator ASN1_TELETEXSTRING

enumerator ASN1_VIDEOTEXSTRING

enumerator ASN1_IA5STRING

enumerator ASN1_UTCTIME

enumerator ASN1_GENERALIZEDTIME

enumerator ASN1_GRAPHICSTRING

enumerator ASN1_VISIBLESTRING

enumerator ASN1_GENERALSTRING

enumerator ASN1_UNIVERSALSTRING

enumerator ASN1_CHARSTRING

enumerator ASN1_BMPSTRING

enum tls_asn1_classes

Values:

enumerator ASN1_UNIVERSAL

tags defined in the ASN.1 standard.

Most use cases on calc will be this.

enumerator ASN1_APPLICATION: tags unique to a particular application.

enumerator ASN1_CONTEXTSPEC: tags that need to be identified within a particular, well-definded context.

enumerator ASN1_PRIVATE: reserved for use by a specific entity for their applications.

enum tls_asn1_forms

Values:

enumerator ASN1_PRIMITIVE: this element should contain no nested elements.

enumerator ASN1_CONSTRUCTED: this element contains nested elements.

Functions

bool tls_asn1_cursor_init(struct tls_asn1_cursor *cursor, const uint8_t *data, size_t len)

Initialize a cursor over a DER buffer.

Parameters:

cursor – Cursor to initialize.
data – Pointer to first DER byte.
len – Number of bytes available from data.

Returns:

true on success, false on invalid arguments.

bool tls_asn1_next(struct tls_asn1_cursor *cursor, struct tls_asn1_tlv *out)

Parse the next TLV from a cursor and advance it.

Note

This API intentionally uses a single boolean return value. Callers that need strict error distinction should track expected structure while parsing (for example: required fields missing before false => parse failure).

Parameters:

cursor – Active cursor.
out – Output TLV descriptor.

Returns:

true if one TLV was parsed successfully.

Returns:

false if:

cursor reached end of data (normal iteration completion), or
input is malformed (invalid DER length/overflow/truncated TLV), or
arguments are invalid.

bool tls_asn1_child_cursor(const struct tls_asn1_tlv *parent, struct tls_asn1_cursor *child)

Create a cursor for a constructed parent TLV’s value bytes.

Note

Call this only when tls_asn1_tag_constructed(parent->tag) is true.

Parameters:

parent – Parent TLV from tls_asn1_next().
child – Output child cursor spanning only parent’s content.

Returns:

true on success.

Returns:

false if:

parent is not constructed, or
arguments are invalid.

uint8_t tls_asn1_tag_number(uint8_t tag): Extract low 5-bit ASN.1 tag number from raw tag byte.

uint8_t tls_asn1_tag_class(uint8_t tag): Extract class bits (ASN1_UNIVERSAL/APPLICATION/CONTEXTSPEC/PRIVATE).

bool tls_asn1_tag_constructed(uint8_t tag): Return true if constructed form bit is set on raw tag byte.

struct tls_asn1_serialization

#include <asn1.h>

Public Members

char *name: field label supplied by caller/parser

uint8_t tag: tag value returned.

size_t len: length of item.

uint8_t *data: pointer to item value.

struct tls_asn1_tlv

#include <asn1.h>

One parsed DER TLV item.

This describes a single ASN.1 element in Tag-Length-Value form. Pointers reference the original input buffer; no copies are made.

Public Members

const uint8_t *tlv: Pointer to the tag byte (start of full TLV).

const uint8_t *value: Pointer to content bytes only (value payload).

size_t len: Content length in bytes (value payload size).

size_t header_len: Header size in bytes (tag + DER length bytes).

uint8_t tag: Raw one-byte ASN.1 tag (class/form/number).

struct tls_asn1_cursor

#include <asn1.h>

Forward-only iterator state over a DER byte span.

Typical usage:

Call tls_asn1_cursor_init() once for a DER buffer.
Repeatedly call tls_asn1_next() until it returns false.
For constructed TLVs (SEQUENCE/SET/context constructed), call tls_asn1_child_cursor() to iterate nested elements.

Public Members

const uint8_t *cur: Current read position.

const uint8_t *end: One-past-end bound for this cursor span.