| 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. |