1 files changed, 141 insertions, 0 deletions
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..39b6b13
--- /dev/null
+++ b/main.go
@@ -0,0 +1,141 @@
+package main
+
+import (
+    "crypto/sha256"
+    "encoding/pem"
+    "flag"
+    "fmt"
+    "os"
+    "strings"
+
+    "github.com/tyler-smith/go-bip39"
+    "golang.org/x/crypto/ed25519"
+    "golang.org/x/crypto/ssh"
+)
+
+const helpMessage = `ssh-bip39gen: generate dd25519 ssh keys from a bip-39 mnemonic
+
+this tool creates deterministic ed25519 ssh key pairs using a 24-word bip-39 mnemonic phrase.
+if no mnemonic is provided, it generates a new one with 256-bit entropy. the mnemonic is your
+key to regenerate the same SSH key pair later - keep it safe!
+
+usage:
+  ssh-bip39gen [-f output_file] [-mnemonic "24-word phrase"]
+
+examples:
+  generate a new key pair (default: id_ed25519):
+    ssh-bip39gen
+
+  generate with custom output file:
+    ssh-bip39gen -f test
+
+  regenerate from a mnemonic:
+    ssh-bip39gen -f test -mnemonic "abandon ability able about ... actress"
+
+flags:
+`
+
+type KeyType string
+
+const (
+    ED25519 KeyType = "ed25519"
+)
+
+type seededRand struct {
+    seed []byte
+    pos  int
+}
+
+func (r *seededRand) Read(p []byte) (n int, err error) {
+    for n < len(p) {
+        counter := uint32(r.pos / len(r.seed))
+        hash := sha256.Sum256(append(r.seed, byte(counter), byte(counter>>8), byte(counter>>16), byte(counter>>24)))
+        n += copy(p[n:], hash[:])
+        r.pos += len(hash)
+    }
+    return len(p), nil
+}
+
+func GenerateEd25519Key(seed []byte) (ed25519.PublicKey, ed25519.PrivateKey, error) {
+    if len(seed) < 32 {
+        return nil, nil, fmt.Errorf("seed too short for ed25519; need 32 bytes, got %d", len(seed))
+    }
+    publicKey, privateKey, err := ed25519.GenerateKey(&seededRand{seed: seed[:32]})
+    return publicKey, privateKey, err
+}
+
+func SaveKeys(privateKey ed25519.PrivateKey, privFile, pubFile string) error {
+    block, err := ssh.MarshalPrivateKey(privateKey, "")
+    if err != nil {
+        return fmt.Errorf("failed to marshal ed25519 private key: %v", err)
+    }
+    privBytes := pem.EncodeToMemory(block)
+
+    pub, err := ssh.NewPublicKey(privateKey.Public())
+    if err != nil {
+        return fmt.Errorf("failed to generate ed25519 public key: %v", err)
+    }
+    pubBytes := ssh.MarshalAuthorizedKey(pub)
+
+    if err := os.WriteFile(privFile, privBytes, 0600); err != nil {
+        return fmt.Errorf("failed to write private key to %s: %v", privFile, err)
+    }
+    if err := os.WriteFile(pubFile, pubBytes, 0644); err != nil {
+        return fmt.Errorf("failed to write public key to %s: %v", pubFile, err)
+    }
+    return nil
+}
+
+func main() {
+    flag.Usage = func() {
+        fmt.Fprint(os.Stderr, helpMessage)
+        flag.PrintDefaults()
+    }
+    
+    mnemonic := flag.String("mnemonic", "", "bip-39 mnemonic phrase (leave empty to generate a new 24-word mnemonic)")
+    outputFile := flag.String("f", "bip39-id_ed25519", "output file for private key (public key will be <file>.pub)")
+    flag.Parse()
+
+    privFile := *outputFile
+    pubFile := *outputFile + ".pub"
+
+    var seed []byte
+    if *mnemonic == "" {
+        entropy, err := bip39.NewEntropy(256)
+        if err != nil {
+            fmt.Printf("error generating entropy: %v\n", err)
+            os.Exit(1)
+        }
+        *mnemonic, err = bip39.NewMnemonic(entropy)
+        if err != nil {
+            fmt.Printf("error generating mnemonic: %v\n", err)
+            os.Exit(1)
+        }
+        fmt.Printf("new mnemonic generated - keep it secure:\n%s\n\n", *mnemonic)
+        seed = bip39.NewSeed(*mnemonic, "")
+    } else {
+        wordCount := len(strings.Fields(*mnemonic))
+        if wordCount != 24 {
+            fmt.Printf("error: mnemonic must contain exactly 24 words, got %d\n", wordCount)
+            os.Exit(1)
+        }
+        if !bip39.IsMnemonicValid(*mnemonic) {
+            fmt.Println("error: invalid mnemonic phrase")
+            os.Exit(1)
+        }
+        seed = bip39.NewSeed(*mnemonic, "")
+    }
+
+    _, priv, err := GenerateEd25519Key(seed)
+    if err != nil {
+        fmt.Printf("error generating ed25519 key: %v\n", err)
+        os.Exit(1)
+    }
+
+    err = SaveKeys(priv, privFile, pubFile)
+    if err != nil {
+        fmt.Printf("error saving keys: %v\n", err)
+        os.Exit(1)
+    }
+    fmt.Printf("ed25519 generated keys:\n  - %s (private)\n  - %s (public)\n", privFile, pubFile)
+}