HPKE: Hybrid Public Key Encryption

This project implements the CFRG's draft-barnes-cfrg-hpke-01, Hybrid Public Key Encryption (HPKE). This branch differs from the original draft in the nonce generation for AEAD. Rather than stateful deriving of the nonce, this branch randomly generates the nonce and appends in the beggining of the ciphertext . For the original stateful implementation, look for branch draft-01.

Authentication modes

Referenced from section 6:

• BASE Encryption to a Public Key: the most basic function of an HPKE scheme is to enable encryption for the holder of a given KEM private key.
• PSK Authentication using a Pre-Shared Key: This variant extends the base mechansism by allowing the recipient to authenticate that the sender possessed a given pre-shared key (PSK). We assume that both parties have been provisioned with both the PSK value "psk" and another octet string "pskID" that is used to identify which PSK should be used.
• AUTH Authentication using an Asymmetric Key: This variant extends the base mechansism by allowing the recipient to authenticate that the sender possessed a given KEM private key. In other words, only two people could have produced this secret, so if the recipient is one, then the sender must be the other.

Ciphersuite configuration

Configuration Name	DH Group	KDF	AEAD
<mode>_X25519_SHA256_AES_GCM_128	Curve25519	HKDF-SHA256	AES-GCM-128
<mode>_X25519_SHA256_ChaCha20Poly1305	Curve25519	HKDF-SHA256	ChaCha20Poly1305
<mode>_X25519_SHA256_XChaCha20Blake2bSIV	Curve25519	HKDF-SHA256	XChaCha20Blake2b
<mode>_P256_SHA256_AES_GCM_128	P-256	HKDF-SHA256	AES-GCM-128
<mode>_P256_SHA256_ChaCha20Poly1305	P-256	HKDF-SHA256	ChaCha20Poly1305
<mode>_P256_SHA256_XChaCha20Blake2bSIV	P-256	HKDF-SHA256	XChaCha20Blake2b
<mode>_P521_SHA512_AES_GCM_256	P-521	HKDF-SHA512	AES-GCM-256
<mode>_P521_SHA512_ChaCha20Poly1305	P-521	HKDF-SHA512	ChaCha20Poly1305
<mode>_P521_SHA256_XChaCha20Blake2bSIV	P-521	HKDF-SHA512	XChaCha20Blake2b

See section 6 for reference.

On top of the AEAD primitives from the draft, implements one more (experimental) AEAD construction with XChaCha20Blake2b in the synthetic IV construction (i.e. no nonce)

Examples: BASE_X25519_SHA256_AES_GCM_128, PSK_P256_SHA256_ChaCha20Poly1305, AUTH_P521_SHA512_ChaCha20Poly1305

Install

• Run go get -u https://github.com/danielhavir/go-hpke

Example

package main

import (
    "bytes"
    "crypto/rand"
    "fmt"

    hpke "github.com/danielhavir/go-hpke"
)

func main() {
    params, _ := hpke.GetParams(hpke.BASE_X25519_SHA256_XChaCha20Blake2bSIV)

    random := rand.Reader
    prv, pub, err := hpke.GenerateKeyPair(params, random)
    if err != nil {
        panic(fmt.Sprintf("failed to generate key pair: %s\n", err))
    }

    msg := []byte("Oh so very secret!")

    ciphertext, ephemeral, err := hpke.EncryptBase(params, random, pub, msg, nil)
    if err != nil {
        panic(fmt.Sprintf("failed to encrypt message: %s\n", err))
    }

    plaintext, err := hpke.DecryptBase(params, prv, ephemeral, ciphertext, nil)
    if err != nil {
        panic(fmt.Sprintf("failed to decrypt ciphertext: %s\n", err))
    }

    if !bytes.Equal(msg, plaintext) {
        panic("authentication failed")
    } else {
        fmt.Println("all good")
    }
}

References

• R. Barnes, K. Bhargavan - Hybrid Public Key Encryption draft-barnes-cfrg-hpke-00
• Go crypto package
• Go ecdh package