1 files changed, 217 insertions, 0 deletions

diff --git a/keys.go b/keys.go
new file mode 100644
index 0000000..3a3fb9c
--- /dev/null
+++ b/keys.go
@@ -0,0 +1,217 @@
+package nostr
+
+import (
+        "crypto/rand"
+        "encoding/hex"
+        "fmt"
+        "strings"
+        "time"
+
+        "github.com/btcsuite/btcd/btcec/v2"
+        "github.com/btcsuite/btcd/btcec/v2/schnorr"
+)
+
+// Key represents a Nostr key, which may be a full private key or public-only.
+// Use GenerateKey or ParseKey for private keys, ParsePublicKey for public-only.
+type Key struct {
+        priv *btcec.PrivateKey // nil for public-only keys
+        pub  *btcec.PublicKey  // always set
+}
+
+// GenerateKey generates a new random private key.
+func GenerateKey() (*Key, error) {
+        var keyBytes [32]byte
+        if _, err := rand.Read(keyBytes[:]); err != nil {
+                return nil, fmt.Errorf("failed to generate random bytes: %w", err)
+        }
+
+        priv, _ := btcec.PrivKeyFromBytes(keyBytes[:])
+        return &Key{
+                priv: priv,
+                pub:  priv.PubKey(),
+        }, nil
+}
+
+// ParseKey parses a private key from hex or nsec (bech32) format.
+func ParseKey(s string) (*Key, error) {
+        var privBytes []byte
+
+        if strings.HasPrefix(s, "nsec1") {
+                hrp, data, err := Bech32Decode(s)
+                if err != nil {
+                        return nil, fmt.Errorf("invalid nsec: %w", err)
+                }
+                if hrp != "nsec" {
+                        return nil, fmt.Errorf("invalid prefix: expected nsec, got %s", hrp)
+                }
+                if len(data) != 32 {
+                        return nil, fmt.Errorf("invalid nsec data length: %d", len(data))
+                }
+                privBytes = data
+        } else {
+                var err error
+                privBytes, err = hex.DecodeString(s)
+                if err != nil {
+                        return nil, fmt.Errorf("invalid hex: %w", err)
+                }
+        }
+
+        if len(privBytes) != 32 {
+                return nil, fmt.Errorf("private key must be 32 bytes, got %d", len(privBytes))
+        }
+
+        priv, _ := btcec.PrivKeyFromBytes(privBytes)
+        return &Key{
+                priv: priv,
+                pub:  priv.PubKey(),
+        }, nil
+}
+
+// ParsePublicKey parses a public key from hex or npub (bech32) format.
+// The returned Key can only verify, not sign.
+func ParsePublicKey(s string) (*Key, error) {
+        var pubBytes []byte
+
+        if strings.HasPrefix(s, "npub1") {
+                hrp, data, err := Bech32Decode(s)
+                if err != nil {
+                        return nil, fmt.Errorf("invalid npub: %w", err)
+                }
+                if hrp != "npub" {
+                        return nil, fmt.Errorf("invalid prefix: expected npub, got %s", hrp)
+                }
+                if len(data) != 32 {
+                        return nil, fmt.Errorf("invalid npub data length: %d", len(data))
+                }
+                pubBytes = data
+        } else {
+                var err error
+                pubBytes, err = hex.DecodeString(s)
+                if err != nil {
+                        return nil, fmt.Errorf("invalid hex: %w", err)
+                }
+        }
+
+        if len(pubBytes) != 32 {
+                return nil, fmt.Errorf("public key must be 32 bytes, got %d", len(pubBytes))
+        }
+
+        pub, err := schnorr.ParsePubKey(pubBytes)
+        if err != nil {
+                return nil, fmt.Errorf("invalid public key: %w", err)
+        }
+
+        return &Key{
+                priv: nil,
+                pub:  pub,
+        }, nil
+}
+
+// CanSign returns true if this key can sign events (has private key).
+func (k *Key) CanSign() bool {
+        return k.priv != nil
+}
+
+// Public returns the public key as a 64-character hex string.
+func (k *Key) Public() string {
+        return hex.EncodeToString(schnorr.SerializePubKey(k.pub))
+}
+
+// Private returns the private key as a 64-character hex string.
+// Returns empty string if this is a public-only key.
+func (k *Key) Private() string {
+        if k.priv == nil {
+                return ""
+        }
+        return hex.EncodeToString(k.priv.Serialize())
+}
+
+// Npub returns the public key in bech32 npub format.
+func (k *Key) Npub() string {
+        pubBytes := schnorr.SerializePubKey(k.pub)
+        npub, _ := Bech32Encode("npub", pubBytes)
+        return npub
+}
+
+// Nsec returns the private key in bech32 nsec format.
+// Returns empty string if this is a public-only key.
+func (k *Key) Nsec() string {
+        if k.priv == nil {
+                return ""
+        }
+        nsec, _ := Bech32Encode("nsec", k.priv.Serialize())
+        return nsec
+}
+
+// Sign signs the event with this key.
+// Sets the PubKey, ID, and Sig fields on the event.
+// Returns an error if this is a public-only key.
+func (k *Key) Sign(event *Event) error {
+        if k.priv == nil {
+                return fmt.Errorf("cannot sign: public-only key")
+        }
+
+        // Set public key
+        event.PubKey = k.Public()
+
+        if event.CreatedAt == 0 {
+                event.CreatedAt = time.Now().Unix()
+        }
+
+        // Compute ID
+        event.SetID()
+
+        // Hash the ID for signing
+        idBytes, err := hex.DecodeString(event.ID)
+        if err != nil {
+                return fmt.Errorf("failed to decode event ID: %w", err)
+        }
+
+        // Sign with Schnorr
+        sig, err := schnorr.Sign(k.priv, idBytes)
+        if err != nil {
+                return fmt.Errorf("failed to sign event: %w", err)
+        }
+
+        event.Sig = hex.EncodeToString(sig.Serialize())
+        return nil
+}
+
+// Verify verifies the event signature.
+// Returns true if the signature is valid, false otherwise.
+func (e *Event) Verify() bool {
+        // Verify ID first
+        if !e.CheckID() {
+                return false
+        }
+
+        // Decode public key
+        pubKeyBytes, err := hex.DecodeString(e.PubKey)
+        if err != nil || len(pubKeyBytes) != 32 {
+                return false
+        }
+
+        pubKey, err := schnorr.ParsePubKey(pubKeyBytes)
+        if err != nil {
+                return false
+        }
+
+        // Decode signature
+        sigBytes, err := hex.DecodeString(e.Sig)
+        if err != nil {
+                return false
+        }
+
+        sig, err := schnorr.ParseSignature(sigBytes)
+        if err != nil {
+                return false
+        }
+
+        // Decode ID (message hash)
+        idBytes, err := hex.DecodeString(e.ID)
+        if err != nil {
+                return false
+        }
+
+        return sig.Verify(idBytes, pubKey)
+}