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implementing-digital-signatures-with-ed25519

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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implementing-digital-signatures-with-ed25519

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Use implementing-digital-signatures-with-ed25519 to design an Ed25519 signing and verification implementation for [artifact or message type] in [language], including key-storage and public-key-validation guidance.

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  • [artifact or message type]
  • [language]

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SKILL.md

name: implementing-digital-signatures-with-ed25519description: 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.domain: cybersecuritysubdomain: cryptographytags: - cryptography- digital-signatures- ed25519- authentication- integrityversion: '1.0'author: mahipallicense: Apache-2.0nist_csf: - PR.DS-01- PR.DS-02- PR.DS-10mitre_attack: - T1600- T1573- T1553

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.

When to Use

  • When deploying or configuring implementing digital signatures with ed25519 capabilities in your environment
  • When establishing security controls aligned to compliance requirements
  • When building or improving security architecture for this domain
  • When conducting security assessments that require this implementation

Prerequisites

  • Familiarity with cryptography concepts and tools
  • Access to a test or lab environment for safe execution
  • Python 3.8+ with required dependencies installed
  • Appropriate authorization for any testing activities

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

PropertyEd25519RSA-3072ECDSA P-256
Security128-bit128-bit128-bit
Public key size32 bytes384 bytes64 bytes
Signature size64 bytes384 bytes64 bytes
Key generation~50 us~100 ms~1 ms
Sign~70 us~5 ms~200 us
Verify~200 us~200 us~500 us
DeterministicYesNo (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