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Mahipal
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Each rewritten description now states both what the skill does (concrete capability, named tools/artifacts) and an explicit when-to-use trigger, improving agent discovery/activation. Grounded in each skill's own body; changes confined to the `description` field only (bodies and all other frontmatter untouched). Produced by a gated audit->rewrite->recheck loop (548 -> 0 flagged) with a sampled anti-invention check (0 ungrounded). Schema: 817/817 pass. Framework-ID gate: 0 defects.
92 lines
3.4 KiB
Markdown
92 lines
3.4 KiB
Markdown
---
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name: implementing-digital-signatures-with-ed25519
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description: Implements digital signatures using the Ed25519 algorithm (Curve25519), covering key-pair generation, signing, signature verification, and security tradeoffs versus RSA and ECDSA. Use when adding message or artifact signing and authentication-integrity checks to a system, or when advising on Ed25519 key properties and validation criteria.
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domain: cybersecurity
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subdomain: cryptography
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tags:
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- cryptography
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- digital-signatures
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- ed25519
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- authentication
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- integrity
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version: '1.0'
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author: mahipal
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license: Apache-2.0
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nist_csf:
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- PR.DS-01
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- PR.DS-02
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- PR.DS-10
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mitre_attack:
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- T1600
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- T1573
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- T1553
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---
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# Implementing Digital Signatures with Ed25519
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## Overview
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Ed25519 is a high-performance digital signature algorithm using the Edwards curve Curve25519. It provides 128-bit security with 64-byte signatures and 32-byte keys, offering significant advantages over RSA and ECDSA including deterministic signatures (no random nonce needed), resistance to side-channel attacks, and fast verification. This skill covers implementing Ed25519 for document signing, code signing, and API authentication.
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## When to Use
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- When deploying or configuring implementing digital signatures with ed25519 capabilities in your environment
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- When establishing security controls aligned to compliance requirements
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- When building or improving security architecture for this domain
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- When conducting security assessments that require this implementation
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## Prerequisites
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- Familiarity with cryptography concepts and tools
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- Access to a test or lab environment for safe execution
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- Python 3.8+ with required dependencies installed
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- Appropriate authorization for any testing activities
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## Objectives
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- Generate Ed25519 key pairs for signing
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- Sign messages and files with Ed25519
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- Verify signatures against public keys
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- Implement multi-signature verification
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- Build a simple code signing system
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- Compare Ed25519 performance with RSA and ECDSA
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## Key Concepts
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### Ed25519 vs RSA vs ECDSA
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| Property | Ed25519 | RSA-3072 | ECDSA P-256 |
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|----------|---------|----------|-------------|
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| Security | 128-bit | 128-bit | 128-bit |
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| Public key size | 32 bytes | 384 bytes | 64 bytes |
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| Signature size | 64 bytes | 384 bytes | 64 bytes |
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| Key generation | ~50 us | ~100 ms | ~1 ms |
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| Sign | ~70 us | ~5 ms | ~200 us |
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| Verify | ~200 us | ~200 us | ~500 us |
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| Deterministic | Yes | No (PSS) | No (unless RFC 6979) |
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### Key Properties
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- **Deterministic**: Same message + key always produces same signature
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- **Collision-resistant**: No separate hash function needed
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- **Side-channel resistant**: Constant-time implementation
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- **Small keys**: 32 bytes each (public and private)
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## Security Considerations
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- Ed25519 does not support key recovery from signatures
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- Verify the full message, not a hash (Ed25519 hashes internally)
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- Public keys must be validated before use (check for low-order points)
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- Private keys should be stored encrypted at rest
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- Ed25519 is not yet approved for all NIST use cases (Ed448 is preferred for federal)
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## Validation Criteria
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- [ ] Key pair generation produces valid Ed25519 keys
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- [ ] Signature verification succeeds for valid message
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- [ ] Signature verification fails for tampered message
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- [ ] Signature verification fails for wrong public key
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- [ ] Deterministic: same input produces same signature
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- [ ] File signing and verification works correctly
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- [ ] Performance meets or exceeds RSA-3072
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