Anthropic-Cybersecurity-Skills/skills/implementing-digital-signatures-with-ed25519/SKILL.md

name, description, domain, subdomain, tags, version, author, license

name	description	domain	subdomain	tags	version	author	license
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	cybersecurity	cryptography	cryptography digital-signatures ed25519 authentication integrity	1.0	mahipal	MIT

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