Initial working PoC

cmd/age-gen-passphrase/main.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"fmt"
+	"time"
+	"unsafe"
+    "errors"
+
+	"crypto/sha256"
+	"golang.org/x/crypto/curve25519"
+
+	"filippo.io/age"
+)
+
+type X25519Identity struct {
+	secretKey, ourPublicKey []byte
+}
+
+func main() {
+	sum := sha256.Sum256([]byte("some secret password phrase"))
+	fmt.Printf("Password hash: %x\n", sum)
+
+    k, err := newX25519IdentityFromScalar(sum[:])
+	if err != nil {
+		fmt.Printf("internal error: %v", err)
+	}
+
+	fmt.Printf("Public key: %s\n", k.Recipient())
+
+	fmt.Printf("# created: %s\n", time.Now().Format(time.RFC3339))
+	fmt.Printf("# public key: %s\n", k.Recipient())
+	fmt.Printf("%s\n", k)
+}
+
+// almost a copy of private function in age/x25519.go
+func newX25519IdentityFromScalar(secretKey []byte) (*age.X25519Identity, error) {
+	if len(secretKey) != curve25519.ScalarSize {
+		return nil, errors.New("invalid X25519 secret key")
+	}
+	i := &X25519Identity{
+		secretKey: make([]byte, curve25519.ScalarSize),
+	}
+	copy(i.secretKey, secretKey)
+	i.ourPublicKey, _ = curve25519.X25519(i.secretKey, curve25519.Basepoint)
+	return (*age.X25519Identity)(unsafe.Pointer(i)), nil
+}

go.mod

@@ -0,0 +1,9 @@
+module github.com/akulij/age-gen-passphrase
+
+go 1.22.2
+
+require (
+	filippo.io/age v1.2.1 // indirect
+	golang.org/x/crypto v0.24.0 // indirect
+	golang.org/x/sys v0.21.0 // indirect
+)

go.sum

@@ -0,0 +1,6 @@
+filippo.io/age v1.2.1 h1:X0TZjehAZylOIj4DubWYU1vWQxv9bJpo+Uu2/LGhi1o=
+filippo.io/age v1.2.1/go.mod h1:JL9ew2lTN+Pyft4RiNGguFfOpewKwSHm5ayKD/A4004=
+golang.org/x/crypto v0.24.0 h1:mnl8DM0o513X8fdIkmyFE/5hTYxbwYOjDS/+rK6qpRI=
+golang.org/x/crypto v0.24.0/go.mod h1:Z1PMYSOR5nyMcyAVAIQSKCDwalqy85Aqn1x3Ws4L5DM=
+golang.org/x/sys v0.21.0 h1:rF+pYz3DAGSQAxAu1CbC7catZg4ebC4UIeIhKxBZvws=
+golang.org/x/sys v0.21.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=