Commit e2c04faf authored by AKASHI Takahiro's avatar AKASHI Takahiro Committed by Tom Rini

doc: add README for asn1 compiler and decoder

This document gives a brief description about ASN1 compiler as well as
ASN1 decoder.
Signed-off-by: default avatarAKASHI Takahiro <takahiro.akashi@linaro.org>
parent ab8a0e06
ASN1
====
Abstract Syntax Notation One (or ASN1) is a standard by ITU-T and ISO/IEC
and used as a description language for defining data structure in
an independent manner.
Any data described in ASN1 notation can be serialized (or encoded) and
de-serialized (or decoded) with well-defined encoding rules.
A combination of ASN1 compiler and ASN1 decoder library function will
provide a function interface for parsing encoded binary into specific
data structure:
1) define data structure in a text file (*.asn1)
2) define "action" routines for specific "tags" defined in (1)
3) generate bytecode as a C file (*.asn1.[ch]) from *.asn1 file
with ASN1 compiler (tools/asn1_compiler)
4) call a ASN1 decoder (asn1_ber_decoder()) with bytecode and data
Usage of ASN1 compiler
----------------------
asn1_compiler [-v] [-d] <grammar-file> <c-file> <hdr-file>
<grammar-file>: ASN1 input file
<c-file>: generated C file
<hdr-file>: generated include file
Usage of ASN1 decoder
---------------------
int asn1_ber_decoder(const struct asn1_decoder *decoder, void *context,
const unsigned char *data, size_t datalen);
@decoder: bytecode binary
@context: context for decoder
@data: data to be parsed
@datalen: size of data
As of writing this, ASN1 compiler and decoder are used to implement
X509 certificate parser, pcks7 message parser and RSA public key parser
for UEFI secure boot.
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