service/crypto.go

package service

import (
	cipher2 "crypto/cipher"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"golang.org/x/crypto/blowfish"
	"io"
)

type BaseMessage struct {
	Signature string
}

func DecryptAndVerify(input []byte, key *rsa.PrivateKey, pub *rsa.PublicKey, signature []byte, v interface{}) error {
	all, err := hex.DecodeString(string(input))
	if err != nil {
		return err
	}

	encPasswordAndIV := all[:512]
	encBody := all[512:]

	passwordAndIV, err := rsa.DecryptPKCS1v15(rand.Reader, key, encPasswordAndIV)

	if err != nil {
		return err
	}

	password := passwordAndIV[:32]
	iv := passwordAndIV[32:40]

	cipher, err := blowfish.NewCipher(password)

	if err != nil {
		return err
	}

	body := make([]byte, len(encBody))
	dec := cipher2.NewCBCDecrypter(cipher, iv)
	dec.CryptBlocks(body, encBody)
	err = json.Unmarshal(Unpad(body), v)

	if err != nil {
		return err
	}

	baseReq, ok := v.(*BaseMessage)
	if !ok {
		return errors.New("non-base request")
	}

	recvSignature, err := hex.DecodeString(baseReq.Signature)
	if err != nil {
		return err
	}

	fingerprint := signature
	fingerprintHashed := sha256.Sum256(fingerprint)
	err = rsa.VerifyPKCS1v15(pub, 0, fingerprintHashed[:], recvSignature)
	return err
}

func EncryptAndSign(v interface{}, key *rsa.PrivateKey, pub *rsa.PublicKey, signature []byte, writer io.Writer) error {
	passwordAndIV := make([]byte, 40)
	_, err := rand.Read(passwordAndIV)
	if err != nil {
		return err
	}

	encPasswordAndIV, err := rsa.EncryptPKCS1v15(rand.Reader, pub, passwordAndIV)
	if err != nil {
		return err
	}

	_, err = writer.Write([]byte(hex.EncodeToString(encPasswordAndIV)))
	if err != nil {
		return err
	}

	password := passwordAndIV[:32]
	iv := passwordAndIV[32:]

	cipher, err := blowfish.NewCipher(password)
	if err != nil {
		return err
	}

	hashedFingerpint := sha256.Sum256(signature)
	plainSignature, err := rsa.SignPKCS1v15(rand.Reader, key, 0, hashedFingerpint[:])
	if err != nil {
		return err
	}

	sign, ok := v.(*BaseMessage)
	if !ok {
		return errors.New("given message can't be signed")
	}
	sign.Signature = hex.EncodeToString(plainSignature)

	body, err := json.Marshal(v)

	if err != nil {
		return err
	}

	encBody := make([]byte, len(body))
	enc := cipher2.NewCBCEncrypter(cipher, iv)
	enc.CryptBlocks(encBody, body)

	copy(encBody[len(encBody):], Pad(encBody))
	writer.Write([]byte(hex.EncodeToString(encBody)))

	return nil
}

func Pad(body []byte) []byte {
	rest := len(body) % 8
	if rest == 0 {
		padLen := GetPad(body)
		if padLen != 0 {
			return []byte{8, 8, 8, 8, 8, 8, 8, 8}
		}

		return []byte{}
	}

	padLen := 8 - rest
	pad := make([]byte, padLen)

	for i := 0; i < padLen; i++ {
		pad[i] = byte(padLen)
	}

	return pad
}

func GetPad(body []byte) int {
	lastIndex := len(body) - 1
	padLen := int(body[lastIndex])
	if 1 < padLen && padLen < 9 {
		isPadding := true

		for i := 0; i < padLen; i++ {
			if body[lastIndex-i] != byte(padLen) {
				isPadding = false
				break
			}
		}

		if isPadding {
			return padLen
		}
	}

	return 0
}

func Unpad(body []byte) []byte {
	return body[:len(body)-GetPad(body)]
}