example/cipher：aes-cbc-with-pkcs7

cipher/aes-cbc-with-pkcs7.go

@@ -0,0 +1,72 @@
+package main
+
+import (
+	"bytes"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/hex"
+	"fmt"
+	"io"
+)
+
+func pkcs7Padding(plainText []byte) []byte {
+	padLen := aes.BlockSize - (len(plainText) % aes.BlockSize)
+	padText := bytes.Repeat([]byte{byte(padLen)}, padLen)
+	return append(plainText, padText...)
+}
+
+func pkcs7Unpadding(plainText []byte) []byte {
+	if textLen := len(plainText); textLen != 0 {
+		padLen := int(plainText[textLen-1])
+		if padLen >= textLen || padLen > aes.BlockSize {
+			return []byte{}
+		}
+		return plainText[:textLen-padLen]
+	}
+	return []byte{}
+}
+
+func aesEncrypter(plainText, key []byte) []byte {
+	plainText = pkcs7Padding(plainText)
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		panic(err)
+	}
+	cipherText := make([]byte, aes.BlockSize+len(plainText))
+	iv := cipherText[:aes.BlockSize]
+	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
+		panic(err)
+	}
+	mode := cipher.NewCBCEncrypter(block, iv)
+	mode.CryptBlocks(cipherText[aes.BlockSize:], plainText)
+	return cipherText
+}
+
+func aesDecrypter(cipherText, key []byte) []byte {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		panic(err)
+	}
+	if len(cipherText) < aes.BlockSize || len(cipherText)%aes.BlockSize != 0 {
+		panic("invalid cipherText")
+	}
+	iv := cipherText[:aes.BlockSize]
+	cipherText = cipherText[aes.BlockSize:]
+	mode := cipher.NewCBCDecrypter(block, iv)
+	mode.CryptBlocks(cipherText, cipherText)
+	plainText := pkcs7Unpadding(cipherText)
+	return plainText
+}
+
+func main() {
+	// 256bit key
+	// key, _ := hex.DecodeString("6368616e6765207468697320706173736368616e676520746869732070617373")
+	// 128bit key
+	key, _ := hex.DecodeString("6368616e676520746869732070617373")
+	plainText := []byte("this is an example of aes-cbc-with-pkcs7")
+	cipherText := aesEncrypter(plainText, key)
+	fmt.Printf("%x\n", cipherText)
+	plainText2 := aesDecrypter(cipherText, key)
+	fmt.Printf("%s\n", plainText2)
+}