diff --git a/README.md b/README.md
index a2731da..e266edb 100644
--- a/README.md
+++ b/README.md
@@ -18,7 +18,7 @@ A modern, comprehensive and efficient utility library of Go.
 
 - Comprehensive, efficient and reusable.
 - Numerous util functions, support string, slice, map, datetime, crypto...
-- Only depend on the go standard library.
+- Only depend on the go standard and golang.org/x library.
 - High unit test coverage for exported functions.
 
 # Encoding
@@ -295,17 +295,24 @@ HMACSHA512("", "") // B936CEE86C9F87AA5D3C6F2E84CB5A4239A5FE50480A6EC66B70AB5B1F
 
 // Encryption functions.
 p := []byte("plaintext")
-key16 := []byte("12345678abcdefgh")
-c, _ := Base64AESCBCEncrypt(p, key16) // A67NhD3RBiNaMgG6HTm8LQ==
-p, _ = Base64AESCBCDecrypt(c, key16)  // plaintext
-
 key8 := []byte("12345678")
-c, _ := Base64DESCBCEncrypt(p, key8) // UZS/y4By6ksePYMBbvZdig==
-p, _ := Base64DESCBCDecrypt(c, key8) // plaintext
+Base64DESCBCEncrypt(p, key8) // UZS/y4By6ksePYMBbvZdig==
+Base64DESCBCDecrypt(c, key8) // plaintext
 
 key24 := []byte("12345678abcdefgh12345678")
-c, _ := Base64TriDESCBCEncrypt(p, key24) // dau0DzmDGQbHasZaOvxxwg==
-p, _ := Base64TriDESCBCDecrypt(c, key24) // plaintext
+Base64TriDESCBCEncrypt(p, key24) // dau0DzmDGQbHasZaOvxxwg==
+Base64TriDESCBCDecrypt(c, key24) // plaintext
+
+key16 := []byte("12345678abcdefgh")
+Base64AESCBCEncrypt(p, key16) // A67NhD3RBiNaMgG6HTm8LQ==
+Base64AESCBCDecrypt(c, key16)  // plaintext
+
+// RSA encryption, decryption, sign and verify signature.
+GenRsaKey(bits int) (prvkey, pubkey []byte, err error)
+RsaEncrypt(pubkey, data []byte) ([]byte, error)
+RsaDecrypt(prvkey, cipher []byte) ([]byte, error)
+RsaSign(prvkey []byte, hash crypto.Hash, data []byte) ([]byte, error)
+RsaVerifySign(pubkey []byte, hash crypto.Hash, data, sig []byte) error
 ```
 
 # Rand
diff --git a/crypto/rsa.go b/crypto/rsa.go
new file mode 100644
index 0000000..2eece65
--- /dev/null
+++ b/crypto/rsa.go
@@ -0,0 +1,126 @@
+package crypto
+
+import (
+	"crypto"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/sha512"
+	"crypto/x509"
+	"encoding/pem"
+	"errors"
+)
+
+// GenRsaKey generates an PKCS#1 RSA keypair of the given bit size in PEM format.
+func GenRsaKey(bits int) (prvkey, pubkey []byte, err error) {
+	// Generates private key.
+	privateKey, err := rsa.GenerateKey(rand.Reader, bits)
+	if err != nil {
+		return
+	}
+	derStream := x509.MarshalPKCS1PrivateKey(privateKey)
+	block := &pem.Block{
+		Type:  "RSA PRIVATE KEY",
+		Bytes: derStream,
+	}
+	prvkey = pem.EncodeToMemory(block)
+
+	// Generates public key from private key.
+	publicKey := &privateKey.PublicKey
+	derPkix, err := x509.MarshalPKIXPublicKey(publicKey)
+	if err != nil {
+		return
+	}
+	block = &pem.Block{
+		Type:  "RSA PUBLIC KEY",
+		Bytes: derPkix,
+	}
+	pubkey = pem.EncodeToMemory(block)
+	return
+}
+
+// RsaEncrypt encrypts data using rsa public key.
+func RsaEncrypt(pubkey, data []byte) ([]byte, error) {
+	block, _ := pem.Decode(pubkey)
+	if block == nil {
+		return nil, errors.New("decode public key error")
+	}
+	pub, err := x509.ParsePKIXPublicKey(block.Bytes)
+	if err != nil {
+		return nil, err
+	}
+	return rsa.EncryptPKCS1v15(rand.Reader, pub.(*rsa.PublicKey), data)
+}
+
+// RsaDecrypt decrypts data using rsa private key.
+func RsaDecrypt(prvkey, cipher []byte) ([]byte, error) {
+	block, _ := pem.Decode(prvkey)
+	if block == nil {
+		return nil, errors.New("decode private key error")
+	}
+	prv, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+	if err != nil {
+		return nil, err
+	}
+	return rsa.DecryptPKCS1v15(rand.Reader, prv, cipher)
+}
+
+// RsaSign signs using private key in PEM format.
+func RsaSign(prvkey []byte, hash crypto.Hash, data []byte) ([]byte, error) {
+	block, _ := pem.Decode(prvkey)
+	if block == nil {
+		return nil, errors.New("decode private key error")
+	}
+	privateKey, err := x509.ParsePKCS1PrivateKey(block.Bytes)
+	if err != nil {
+		return nil, err
+	}
+
+	// MD5 and SHA1 are not supported as they are not secure.
+	var hashed []byte
+	switch hash {
+	case crypto.SHA224:
+		h := sha256.Sum224(data)
+		hashed = h[:]
+	case crypto.SHA256:
+		h := sha256.Sum256(data)
+		hashed = h[:]
+	case crypto.SHA384:
+		h := sha512.Sum384(data)
+		hashed = h[:]
+	case crypto.SHA512:
+		h := sha512.Sum512(data)
+		hashed = h[:]
+	}
+	return rsa.SignPKCS1v15(rand.Reader, privateKey, hash, hashed)
+}
+
+// RsaVerifySign verifies signature using public key in PEM format.
+func RsaVerifySign(pubkey []byte, hash crypto.Hash, data, sig []byte) error {
+	block, _ := pem.Decode(pubkey)
+	if block == nil {
+		return errors.New("decode public key error")
+	}
+	pub, err := x509.ParsePKIXPublicKey(block.Bytes)
+	if err != nil {
+		return err
+	}
+
+	// SHA1 and MD5 are not supported as they are not secure.
+	var hashed []byte
+	switch hash {
+	case crypto.SHA224:
+		h := sha256.Sum224(data)
+		hashed = h[:]
+	case crypto.SHA256:
+		h := sha256.Sum256(data)
+		hashed = h[:]
+	case crypto.SHA384:
+		h := sha512.Sum384(data)
+		hashed = h[:]
+	case crypto.SHA512:
+		h := sha512.Sum512(data)
+		hashed = h[:]
+	}
+	return rsa.VerifyPKCS1v15(pub.(*rsa.PublicKey), hash, hashed, sig)
+}
diff --git a/crypto/rsa_test.go b/crypto/rsa_test.go
new file mode 100644
index 0000000..a57d591
--- /dev/null
+++ b/crypto/rsa_test.go
@@ -0,0 +1,73 @@
+package crypto
+
+import (
+	"crypto"
+	"testing"
+
+	"github.com/dablelv/go-huge-util/internal"
+)
+
+func TestRsaEncryptDecrypt(t *testing.T) {
+	assert := internal.NewAssert(t, "RsaEncryptDecrypt")
+
+	data := []byte("foo")
+
+	// Encrypt and decrypt data using 2048 bits length key.
+	prvkey, pubkey, err := GenRsaKey(2048)
+	assert.IsNil(err)
+
+	// Encrypt data.
+	cipher, err := RsaEncrypt(pubkey, data)
+	assert.IsNil(err)
+	assert.Equal(2048/8, len(cipher))
+
+	// Decrypt data.
+	plain, err := RsaDecrypt(prvkey, cipher)
+	assert.IsNil(err)
+	assert.Equal(data, plain)
+
+	// Encrypt and decrypt data using 4096 bits length key.
+	prvkey, pubkey, err = GenRsaKey(4096)
+	assert.IsNil(err)
+
+	// Encrypt data.
+	cipher, err = RsaEncrypt(pubkey, data)
+	assert.IsNil(err)
+	assert.Equal(4096/8, len(cipher))
+
+	// Decrypt data.
+	plain, err = RsaDecrypt(prvkey, cipher)
+	assert.IsNil(err)
+	assert.Equal(data, plain)
+
+	// Encrypt and decrypt data using 8192 bits length key.
+	prvkey, pubkey, err = GenRsaKey(8192)
+	assert.IsNil(err)
+
+	// Encrypt data.
+	cipher, err = RsaEncrypt(pubkey, data)
+	assert.IsNil(err)
+	assert.Equal(8192/8, len(cipher))
+
+	// Decrypt data.
+	plain, err = RsaDecrypt(prvkey, cipher)
+	assert.IsNil(err)
+	assert.Equal(data, plain)
+}
+
+func TestRsaSignAndVerify(t *testing.T) {
+	assert := internal.NewAssert(t, "RsaSignAndVerify")
+
+	msg := []byte("foo")
+	prvkey, pubkey, err := GenRsaKey(2048)
+	assert.IsNil(err)
+
+	// Using SHA256 to hash msg and then use rsa private key to sign.
+	sig, err := RsaSign(prvkey, crypto.SHA256, msg)
+	assert.IsNil(err)
+	assert.Equal(2048/8, len(sig))
+
+	// Using public key to verify signature.
+	err = RsaVerifySign(pubkey, crypto.SHA256, msg, sig)
+	assert.IsNil(err)
+}
diff --git a/go.mod b/go.mod
index 7ea9f78..2456bc1 100644
--- a/go.mod
+++ b/go.mod
@@ -1,4 +1,4 @@
-module github.com/dablelv/go-huge-util
+module github.com/dablelv/cyan
 
 go 1.19