1 files changed, 150 insertions, 0 deletions
diff --git a/pkgs/yokey/crypto.go b/pkgs/yokey/crypto.go
new file mode 100644
index 0000000..df6e4ec
--- /dev/null
+++ b/pkgs/yokey/crypto.go
@@ -0,0 +1,150 @@
+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
+}