Verify OTP

• Verify OTP entered by the end user
  • otp value have to be passed in encrypted manner
  • Encrytion logic as follow
    • Encryption Algorithm AES CBC 256 bit, with no Initial Vector
    • Use basic authentication client_id/username as encryption key
    • Use first 16 characters of the authentication secret for IV
    • Use hex encoding

Sample Go Code

package main

import (
    "bytes"
    "crypto/aes"
    "crypto/cipher"
    "encoding/base64"
    "fmt"
    "strings"
)

const IV = "NDMbfRhOsN3QNGKx"
const KEY = "zDYWhP5keEvuGMWxlWBQCym43jIBYKJY"

func main() {
    EncryptTest("926946")
}

func EncryptTest(plaintext string) {
    key := []byte(KEY)
    encryptAES, _ := EncryptAES(plaintext, key, []byte(IV))
    _, err := DecryptAES(encryptAES, key, []byte(IV))
    if err != nil {
        fmt.Println(err.Error())
    }

    fmt.Println("result: " + encryptAES)
}

// EncryptAES Encrypts the given plain text using the given key
// returns a hex encoded string of the AES encrypted string
func EncryptAES(content string, encryptionKey []byte, IV []byte) (string, error) {
    paddedPlaintext := PKCS5Padding([]byte(content), aes.BlockSize)
    block, err := aes.NewCipher(encryptionKey)

    if err != nil {
        return "", err
    }

    ciphertext := make([]byte, len(paddedPlaintext))
    mode := cipher.NewCBCEncrypter(block, IV)
    mode.CryptBlocks(ciphertext, paddedPlaintext)

    return base64.StdEncoding.EncodeToString(ciphertext), nil
}

// DecryptAES decrypts a given hex encoded AES encrypted string
// using the key given
func DecryptAES(cipherText string, encryptionKey []byte, IV []byte) (string, error) {
    block, err := aes.NewCipher(encryptionKey)
    if err != nil {
        return "", err
    }

    c, err := base64.StdEncoding.DecodeString(cipherText)
    if err != nil {
        return "", err
    }

    mode := cipher.NewCBCDecrypter(block, IV)
    mode.CryptBlocks(c, c)

    return strings.TrimSpace(string(c)), err
}

// PKCS5Padding adds the necessary padding for the given
// data
func PKCS5Padding(cipherText []byte, blockSize int) []byte {
    padding := blockSize - len(cipherText)%blockSize
    padText := bytes.Repeat([]byte{byte(padding)}, padding)
    return append(cipherText, padText...)
}