Why a 202-Character License Key Uses ECDSA P-256 Instead of Ed25519 or RSA
A developer building offline license verification for a .NET desktop application evaluated Ed25519, RSA, and ECDSA P-256 before selecting the last option. The decision was driven by the requirement for zero external dependencies, keys short enough for manual entry from email, and support for key rotation without breaking existing licenses. Although Ed25519 offers faster verification and a smaller public key, it is absent from System.Security.Cryptography in both .NET 8 and .NET 10, with API approval only targeted for version 11. RSA-2048 produces signatures too long for practical use, resulting in a 571-character Base32 string that users would find cumbersome. ECDSA P-256 with SHA-256 delivers a fixed 64-byte signature that becomes a manageable 202-character key when encoded in Base32, while remaining fully available in the runtime. The article also covers performance measurements, the risks of ECDSA nonce generation, and the deliberate choice of the IEEE P1363 signature format to guarantee fixed-length output.
HabrJul 28, 2026Translated from Russian