asn1_encoder.c | Explore in Territory

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Simple encoder primitives for ASN.1 BER/DER/CER
 *
 * Copyright (C) 2019 [email protected]
 */

#include <linux/asn1_encoder.h>
#include <linux/bug.h>
#include <linux/string.h>
#include <linux/module.h>

/**
 * asn1_encode_integer() - encode positive integer to ASN.1
 * @data:	pointer to the pointer to the data
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @integer:	integer to be encoded
 *
 * This is a simplified encoder: it only currently does
 * positive integers, but it should be simple enough to add the
 * negative case if a use comes along.
 */
unsigned char *
asn1_encode_integer(unsigned char *data, const unsigned char *end_data,
		    s64 integer)
{ … }
EXPORT_SYMBOL_GPL(…);

/* calculate the base 128 digit values setting the top bit of the first octet */
static int asn1_encode_oid_digit(unsigned char **_data, int *data_len, u32 oid)
{ … }

/**
 * asn1_encode_oid() - encode an oid to ASN.1
 * @data:	position to begin encoding at
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @oid:	array of oids
 * @oid_len:	length of oid array
 *
 * this encodes an OID up to ASN.1 when presented as an array of OID values
 */
unsigned char *
asn1_encode_oid(unsigned char *data, const unsigned char *end_data,
		u32 oid[], int oid_len)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * asn1_encode_length() - encode a length to follow an ASN.1 tag
 * @data: pointer to encode at
 * @data_len: pointer to remaining length (adjusted by routine)
 * @len: length to encode
 *
 * This routine can encode lengths up to 65535 using the ASN.1 rules.
 * It will accept a negative length and place a zero length tag
 * instead (to keep the ASN.1 valid).  This convention allows other
 * encoder primitives to accept negative lengths as singalling the
 * sequence will be re-encoded when the length is known.
 */
static int asn1_encode_length(unsigned char **data, int *data_len, int len)
{ … }

/**
 * asn1_encode_tag() - add a tag for optional or explicit value
 * @data:	pointer to place tag at
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @tag:	tag to be placed
 * @string:	the data to be tagged
 * @len:	the length of the data to be tagged
 *
 * Note this currently only handles short form tags < 31.
 *
 * Standard usage is to pass in a @tag, @string and @length and the
 * @string will be ASN.1 encoded with @tag and placed into @data.  If
 * the encoding would put data past @end_data then an error is
 * returned, otherwise a pointer to a position one beyond the encoding
 * is returned.
 *
 * To encode in place pass a NULL @string and -1 for @len and the
 * maximum allowable beginning and end of the data; all this will do
 * is add the current maximum length and update the data pointer to
 * the place where the tag contents should be placed is returned.  The
 * data should be copied in by the calling routine which should then
 * repeat the prior statement but now with the known length.  In order
 * to avoid having to keep both before and after pointers, the repeat
 * expects to be called with @data pointing to where the first encode
 * returned it and still NULL for @string but the real length in @len.
 */
unsigned char *
asn1_encode_tag(unsigned char *data, const unsigned char *end_data,
		u32 tag, const unsigned char *string, int len)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * asn1_encode_octet_string() - encode an ASN.1 OCTET STRING
 * @data:	pointer to encode at
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @string:	string to be encoded
 * @len:	length of string
 *
 * Note ASN.1 octet strings may contain zeros, so the length is obligatory.
 */
unsigned char *
asn1_encode_octet_string(unsigned char *data,
			 const unsigned char *end_data,
			 const unsigned char *string, u32 len)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * asn1_encode_sequence() - wrap a byte stream in an ASN.1 SEQUENCE
 * @data:	pointer to encode at
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @seq:	data to be encoded as a sequence
 * @len:	length of the data to be encoded as a sequence
 *
 * Fill in a sequence.  To encode in place, pass NULL for @seq and -1
 * for @len; then call again once the length is known (still with NULL
 * for @seq). In order to avoid having to keep both before and after
 * pointers, the repeat expects to be called with @data pointing to
 * where the first encode placed it.
 */
unsigned char *
asn1_encode_sequence(unsigned char *data, const unsigned char *end_data,
		     const unsigned char *seq, int len)
{ … }
EXPORT_SYMBOL_GPL(…);

/**
 * asn1_encode_boolean() - encode a boolean value to ASN.1
 * @data:	pointer to encode at
 * @end_data:	end of data pointer, points one beyond last usable byte in @data
 * @val:	the boolean true/false value
 */
unsigned char *
asn1_encode_boolean(unsigned char *data, const unsigned char *end_data,
		    bool val)
{ … }
EXPORT_SYMBOL_GPL(…);

MODULE_DESCRIPTION(…) …;
MODULE_LICENSE(…) …;
linux/lib/asn1_encoder.c
