add comments to crypto package

pkg/crypto/crypto.go

@@ -16,17 +16,28 @@ import (
 	"golang.org/x/crypto/sha3"
 )
 
-var keyTypeSecp256k1 = "Secp256k1"
+var keyTypeSecp256k1 = "secp256k1"
 
+// GenerateSecp256k1Key generates an ECDSA private key using
+// secp256k1 elliptic curve.
 func GenerateSecp256k1Key() (*ecdsa.PrivateKey, error) {
 	return ecdsa.GenerateKey(btcec.S256(), rand.Reader)
 }
 
+// NewAddress constructs a Swarm Address from ECDSA private key.
+func NewAddress(p ecdsa.PublicKey) swarm.Address {
+	d := elliptic.Marshal(btcec.S256(), p.X, p.Y)
+	return swarm.NewAddress(keccak256(d))
+}
+
+// privateKey holds information about Swarm private key for mashaling.
 type privateKey struct {
 	Type string `json:"type"`
 	Key  []byte `json:"key"`
 }
 
+// MarshalSecp256k1PrivateKey marshals secp256k1 ECDSA private key
+// that can be unmarshaled by UnmarshalPrivateKey.
 func MarshalSecp256k1PrivateKey(k *ecdsa.PrivateKey) ([]byte, error) {
 	return json.Marshal(privateKey{
 		Type: keyTypeSecp256k1,
@@ -34,6 +45,7 @@ func MarshalSecp256k1PrivateKey(k *ecdsa.PrivateKey) ([]byte, error) {
 	})
 }
 
+// UnmarshalPrivateKey unmarshals ECDSA private key from encoded data.
 func UnmarshalPrivateKey(data []byte) (*ecdsa.PrivateKey, error) {
 	var pk privateKey
 	if err := json.Unmarshal(data, &pk); err != nil {
@@ -47,6 +59,7 @@ func UnmarshalPrivateKey(data []byte) (*ecdsa.PrivateKey, error) {
 	}
 }
 
+// decodeSecp256k1PrivateKey decodes raw ECDSA private key.
 func decodeSecp256k1PrivateKey(data []byte) (*ecdsa.PrivateKey, error) {
 	if l := len(data); l != btcec.PrivKeyBytesLen {
 		return nil, fmt.Errorf("secp256k1 data size %d expected %d", l, btcec.PrivKeyBytesLen)
@@ -55,11 +68,7 @@ func decodeSecp256k1PrivateKey(data []byte) (*ecdsa.PrivateKey, error) {
 	return (*ecdsa.PrivateKey)(privk), nil
 }
 
-func NewAddress(p ecdsa.PublicKey) swarm.Address {
-	d := elliptic.Marshal(btcec.S256(), p.X, p.Y)
-	return swarm.NewAddress(keccak256(d))
-}
-
+// keccak256 calculates a hash sum from provided data.
 func keccak256(data ...[]byte) []byte {
 	d := sha3.New256()
 	for _, b := range data {