Agent-Skills.md

Agent Skills: Implementing Digital Signatures with Ed25519

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 ove

UncategorizedID: autohandai/community-skills/implementing-digital-signatures-with-ed25519

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autohandai/community-skills
autohandaiLicense: Apache-2.0
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implementing-digital-signatures-with-ed25519/SKILL.md

Skill Metadata

Name
implementing-digital-signatures-with-ed25519
Description
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 ove

Implementing Digital Signatures with Ed25519

Overview

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.

Objectives

  • Generate Ed25519 key pairs for signing
  • Sign messages and files with Ed25519
  • Verify signatures against public keys
  • Implement multi-signature verification
  • Build a simple code signing system
  • Compare Ed25519 performance with RSA and ECDSA

Key Concepts

Ed25519 vs RSA vs ECDSA

| Property | Ed25519 | RSA-3072 | ECDSA P-256 | |----------|---------|----------|-------------| | Security | 128-bit | 128-bit | 128-bit | | Public key size | 32 bytes | 384 bytes | 64 bytes | | Signature size | 64 bytes | 384 bytes | 64 bytes | | Key generation | ~50 us | ~100 ms | ~1 ms | | Sign | ~70 us | ~5 ms | ~200 us | | Verify | ~200 us | ~200 us | ~500 us | | Deterministic | Yes | No (PSS) | No (unless RFC 6979) |

Key Properties

  • Deterministic: Same message + key always produces same signature
  • Collision-resistant: No separate hash function needed
  • Side-channel resistant: Constant-time implementation
  • Small keys: 32 bytes each (public and private)

Security Considerations

  • Ed25519 does not support key recovery from signatures
  • Verify the full message, not a hash (Ed25519 hashes internally)
  • Public keys must be validated before use (check for low-order points)
  • Private keys should be stored encrypted at rest
  • Ed25519 is not yet approved for all NIST use cases (Ed448 is preferred for federal)

Validation Criteria

  • [ ] Key pair generation produces valid Ed25519 keys
  • [ ] Signature verification succeeds for valid message
  • [ ] Signature verification fails for tampered message
  • [ ] Signature verification fails for wrong public key
  • [ ] Deterministic: same input produces same signature
  • [ ] File signing and verification works correctly
  • [ ] Performance meets or exceeds RSA-3072