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package main
import (
"crypto"
"crypto/ed25519"
"crypto/rand"
"crypto/sha256"
"encoding/base64"
"encoding/pem"
"io"
"strings"
"golang.org/x/crypto/curve25519"
"golang.org/x/crypto/hkdf"
"golang.org/x/crypto/ssh"
"pault.ag/go/sshsig"
)
const sshsigContext = "sshsig-key-v1"
func deriveKey(master []byte, info string, length int) []byte {
h := hkdf.New(sha256.New, master, []byte("fixed-salt"), []byte(info))
out := make([]byte, length)
if _, err := io.ReadFull(h, out); err != nil {
panic(err)
}
return out
}
func buildInfo(baseInfo, context string) string {
trimmed := strings.TrimSpace(context)
if trimmed == "" {
return baseInfo
}
return baseInfo + ":" + trimmed
}
func deriveEd25519(master []byte, context string) (string, []byte) {
seed := deriveKey(master, buildInfo("ed25519-key-v1", context), 32)
priv := ed25519.NewKeyFromSeed(seed)
pub := priv.Public().(ed25519.PublicKey)
sshPub, err := ssh.NewPublicKey(pub)
if err != nil {
panic(err)
}
privBlock, err := ssh.MarshalPrivateKey(priv, "")
if err != nil {
panic(err)
}
return string(ssh.MarshalAuthorizedKey(sshPub)), pem.EncodeToMemory(privBlock)
}
func deriveWireGuard(master []byte, context string) (string, string) {
priv := deriveKey(master, buildInfo("wireguard-key-v1", context), 32)
pub, _ := curve25519.X25519(priv, curve25519.Basepoint)
return base64.StdEncoding.EncodeToString(pub), base64.StdEncoding.EncodeToString(priv)
}
const passwordCharset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@$%^&*"
const passwordLength = 14
func derivePassword(master []byte, seed string) string {
return derivePasswordWithContext(master, seed, "")
}
func derivePasswordWithContext(master []byte, seed, context string) string {
info := buildInfo("password-v1:"+seed, context)
stream := hkdf.New(sha256.New, master, []byte("my-fixed-salt"), []byte(info))
out := make([]byte, 0, passwordLength)
buf := make([]byte, 64)
maxMultiple := byte(256 / len(passwordCharset) * len(passwordCharset))
for len(out) < passwordLength {
if _, err := io.ReadFull(stream, buf); err != nil {
panic(err)
}
for _, b := range buf {
if b >= maxMultiple {
continue
}
out = append(out, passwordCharset[int(b)%len(passwordCharset)])
if len(out) == passwordLength {
break
}
}
}
return string(out)
}
func deriveSSHSigSigner(master []byte) ssh.Signer {
_, privPem := deriveEd25519(master, sshsigContext)
rawPriv, err := ssh.ParseRawPrivateKey(privPem)
if err != nil {
panic(err)
}
signer, err := ssh.NewSignerFromKey(rawPriv)
if err != nil {
panic(err)
}
return signer
}
func signSSHSig(master []byte, namespace string, message []byte) []byte {
signer := deriveSSHSigSigner(master)
h := crypto.SHA512.New()
if _, err := h.Write(message); err != nil {
panic(err)
}
sig, err := sshsig.Sign(rand.Reader, signer, []byte(namespace), sshsig.HashAlgoSHA512, h.Sum(nil))
if err != nil {
panic(err)
}
return sig
}
func verifySSHSig(master []byte, namespace string, message, signature []byte) error {
signer := deriveSSHSigSigner(master)
pub := signer.PublicKey()
parsedSig, err := sshsig.ParseSignature(signature)
if err != nil {
return err
}
h := crypto.SHA512.New()
if _, err := h.Write(message); err != nil {
return err
}
return sshsig.Verify(pub, []byte(namespace), sshsig.HashAlgoSHA512, h.Sum(nil), parsedSig)
}
func generateMasterKeyBytes() []byte {
key := make([]byte, 32)
rand.Read(key)
return key
}
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