TOOLS / ENCRYPTION

Diffie-Hellman
(DH & ECDH)

Generate key pairs and compute shared secrets.

Key exchange

Classic DHECDH

RFC 3526 group

MODP 2048-bit (Group 14)MODP 3072-bit (Group 15)MODP 4096-bit (Group 16)

Prime p (HEX)

Generator g (HEX)

Classic DH

Supports RFC 3526 Groups 14, 15 and 16 with generator 02. Custom groups are not supported. Peer keys are checked against the prime-order subgroup. The secret is padded to the prime’s byte length.

ECDH

Public keys use compressed or uncompressed SEC1 encoding. The shared secret is the X coordinate: 32 bytes for P-256 and secp256k1, 48 for P-384, or 66 for P-521.

Using the result

Each party uses their own private key and the other party’s public key. Both must use the same group or curve.

The raw shared secret is not a finished encryption key. Use HKDF with your protocol’s salt and context. Key exchange alone does not authenticate the peer.

Classic DH uses JavaScript BigInt arithmetic for this test calculator; it is not a constant-time production implementation.

RFC 3526 - MODP groups ↗
noble-curves ↗ · MIT license

Calculator reference

Verification evidence and limitations →

What it calculates

Computes a shared secret from a private key and a peer’s public key.

Inputs and methods

Classic DH groups 14/15/16, or ECDH on P-256/P-384/P-521/secp256k1.

Worked example

Classic DH group 14: private key 02, peer public key 04.

Shared secret: 10, left-padded with zeros to 256 bytes

Specification and limits

The tiny private value is for demonstration only. Raw secrets need a KDF; DH alone does not authenticate peers.

RFC 3526 ↗