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
