asn1
Reference for ASN.1 notation, BER (Basic Encoding Rules), and DER (Distinguished Encoding Rules). Use when decoding/encoding binary data, debugging ASN.1 structures, or understanding PKCS standards.
Best use case
asn1 is best used when you need a repeatable AI agent workflow instead of a one-off prompt.
Reference for ASN.1 notation, BER (Basic Encoding Rules), and DER (Distinguished Encoding Rules). Use when decoding/encoding binary data, debugging ASN.1 structures, or understanding PKCS standards.
Teams using asn1 should expect a more consistent output, faster repeated execution, less prompt rewriting.
When to use this skill
- You want a reusable workflow that can be run more than once with consistent structure.
When not to use this skill
- You only need a quick one-off answer and do not need a reusable workflow.
- You cannot install or maintain the underlying files, dependencies, or repository context.
Installation
Claude Code / Cursor / Codex
Manual Installation
- Download SKILL.md from GitHub
- Place it in
.claude/skills/asn1/SKILL.mdinside your project - Restart your AI agent — it will auto-discover the skill
How asn1 Compares
| Feature / Agent | asn1 | Standard Approach |
|---|---|---|
| Platform Support | Not specified | Limited / Varies |
| Context Awareness | High | Baseline |
| Installation Complexity | Unknown | N/A |
Frequently Asked Questions
What does this skill do?
Reference for ASN.1 notation, BER (Basic Encoding Rules), and DER (Distinguished Encoding Rules). Use when decoding/encoding binary data, debugging ASN.1 structures, or understanding PKCS standards.
Where can I find the source code?
You can find the source code on GitHub using the link provided at the top of the page.
SKILL.md Source
# ASN.1, BER, and DER This skill provides reference material for Abstract Syntax Notation One (ASN.1) and its encoding rules (BER/DER). ## Quick Reference ### Universal Tags | Tag (Hex) | Type | | :--- | :--- | | `01` | BOOLEAN | | `02` | INTEGER | | `03` | BIT STRING | | `04` | OCTET STRING | | `05` | NULL | | `06` | OBJECT IDENTIFIER | | `10` | SEQUENCE / SEQUENCE OF | | `11` | SET / SET OF | | `13` | PrintableString | | `14` | T61String | | `16` | IA5String | | `17` | UTCTime | ### Identifier Octet (First Byte) Bits 8-7: Class - `00`: Universal - `01`: Application - `10`: Context-specific - `11`: Private Bit 6: PC (Primitive/Constructed) - `0`: Primitive (Value is directly in contents) - `1`: Constructed (Contents are nested TLV elements) Bits 5-1: Tag Number (if < 31) ## Detailed Guide For a comprehensive guide on notation, encoding rules, and specific type handling, read the bundled reference: `references/guide.md` ### Contents of the Guide: 1. **Introduction**: Overview of OSI, ASN.1, BER, DER. 2. **ASN.1 Notation**: Simple types, structured types, tagging. 3. **BER**: Primitive vs. Constructed, Definite vs. Indefinite length. 4. **DER**: subset of BER for unique encoding (Canonical). 5. **Type-Specific Encodings**: Detailed breakdown of how to encode INTEGER, BIT STRING, SEQUENCE, etc. 6. **Example**: Walkthrough of an X.500 Name encoding. ## Common Operations ### Deciphering a Tag If you encounter byte `0x30`: - Binary: `0011 0000` - Class: `00` (Universal) - P/C: `1` (Constructed) - Tag: `10000` (16 -> SEQUENCE) If you encounter byte `0xA0`: - Binary: `1010 0000` - Class: `10` (Context-specific) - P/C: `1` (Constructed) - Tag: `00000` (0 -> [0]) ### Variable Lengths - **Short Form**: `0x00` - `0x7F` (0-127 bytes). - **Long Form**: Bit 8 is 1. Bits 7-1 = number of length bytes following. - Example: `0x81 0x80` -> Length is in next 1 byte (`0x81`), value is `0x80` (128). - Example: `0x82 0x01 0x00` -> Length is in next 2 bytes (`0x82`), value is `0x0100` (256).
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