I have a scenario where I need to use RSA public key encryption standard with JavaScript and Golang. I need to encrypt data in JavaScript using public key and decrypt the same in Golang using the private key. I tried using PKCS#1(travst library for JavaScript and crypto/rsa for Golang), but failed in decryption. Can anyone suggest solutions for this?

I tried all possible solutions and researched many documents, but still I couldn't find a proper method. If I do encrypt and decrypt within golang, its working fine. But there is some integration problem between javascript and golang. I am not sure about the padding methodology used in javasript.

This is my golang code to decrypt:

func Decrypt(encryptedData, label []byte) (decryptedData []byte) {
var err error
var block *pem.Block
var private_key *rsa.PrivateKey

if block, _ = pem.Decode([]byte(privatKeyData)); block == nil || block.Type != "RSA PRIVATE KEY" { //privatKeyData is in string format
    log.Fatal("No valid PEM data found")
}

//Read Private Key
if private_key, err = x509.ParsePKCS1PrivateKey(block.Bytes); err != nil {
    log.Fatalf("Private key can't be decoded: %s", err)
}

//Decrypt
if decrypted, err = rsa.DecryptPKCS1v15(rand.Reader, private_key, encryptedData); err != nil {
        log.Println(err)
}
return
}

I have a scenario where I need to use RSA public key encryption standard with JavaScript and Golang. I need to encrypt data in JavaScript using public key and decrypt the same in Golang using the private key. I tried using PKCS#1(travst library for JavaScript and crypto/rsa for Golang), but failed in decryption. Can anyone suggest solutions for this?

I tried all possible solutions and researched many documents, but still I couldn't find a proper method. If I do encrypt and decrypt within golang, its working fine. But there is some integration problem between javascript and golang. I am not sure about the padding methodology used in javasript.

This is my golang code to decrypt:

func Decrypt(encryptedData, label []byte) (decryptedData []byte) {
var err error
var block *pem.Block
var private_key *rsa.PrivateKey

if block, _ = pem.Decode([]byte(privatKeyData)); block == nil || block.Type != "RSA PRIVATE KEY" { //privatKeyData is in string format
    log.Fatal("No valid PEM data found")
}

//Read Private Key
if private_key, err = x509.ParsePKCS1PrivateKey(block.Bytes); err != nil {
    log.Fatalf("Private key can't be decoded: %s", err)
}

//Decrypt
if decrypted, err = rsa.DecryptPKCS1v15(rand.Reader, private_key, encryptedData); err != nil {
        log.Println(err)
}
return
}

• javascript
• go
• cryptography
• rsa
• public-key-encryption

• 2 can you post the error received? or show us the decryption result. – Endre Simo Commented Mar 17, 2016 at 8:10
• 1 @SimoEndre Error: crypto/rsa: decryption error (i just received this error) – Sujai Sivasamy Commented Mar 17, 2016 at 9:34
• 1 I tried decoding the encrypted data from base64 format and decrypted it, but still received the same error – Sujai Sivasamy Commented Mar 17, 2016 at 9:37
• Share your code, to have an idea on the issue. – Endre Simo Commented Mar 17, 2016 at 9:51
• Assume you mean jsencrypt library? – Mark Commented Mar 19, 2016 at 9:45

2 Answers 2

It's possible to encrypt in javascript and decrypt in Go. Using the library you refer to, jsencrypt:

Create public & private key pair:

openssl genrsa -out key.pem
openssl rsa -in key.pem -pubout > pub.pem

Encryption in javascript:

var encrypt = new JSEncrypt();
encrypt.setPublicKey($('#pubkey').val());

var encrypted = encrypt.encrypt($('#message').val());

$.post("/decrypt", encrypted, function(response) {
    $("#decrypted").val(response);
});

Decryption in Go:

func handleDecrypt(w http.ResponseWriter, r *http.Request) {
    decoder := base64.NewDecoder(base64.StdEncoding, r.Body)
    defer r.Body.Close()
    encrypted, err := ioutil.ReadAll(decoder)
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }
    data, err := rsa.DecryptPKCS1v15(rand.Reader, privateKey, encrypted)
    if err != nil {
        http.Error(w, "decrypt error", http.StatusBadRequest)
        log.Println(err)
        return
    }
    fmt.Fprint(w, string(data))
}

Update: the privateKey variable is a *rsa.PrivateKey derived from the private key file created by openssl, in this case the "key.pem" file. A pem file is a Base64 encoded DER certificate, eg, -----BEGIN RSA PRIVATE KEY----- and -----END RSA PRIVATE KEY----- show a private key in PEM format. Go standard library provides the x509.ParsePKCS1PrivateKey() method to parse a pem encoded key from a byte slice.

So loading the key into Go might look something like this:

keyBytes, err := ioutil.ReadFile("path/to/key.pem")
if err != nil { ... }

privateKey, err := x509.ParsePKCS1PrivateKey(keyBytes)
if err != nil { ... }

1：You can encrypt cleartext in javascript reference from.

https://github./travist/jsencrypt

var encrypt = new JSEncrypt();
encrypt.setPublicKey($('#pubkey').val());
var encrypted = encrypt.encrypt($('#input').val());

2：Be aware of that the jsencrypt has already done encrypt and base64encode.

Be aware of that jsencrypt use PKCS1 not OAEP

3: Base64decode in golang and decrypt message from step 1.

var encrypted := 'change this to the encrypted text your js sent'
privateKey,_ = ioutil.ReadFile("private.pem")
cipherText,_ := base64.StdEncoding.DecodeString(encrypted)
originText,_ :=RsaDecrypt([]byte(cipherText))

decrypt function

func RsaDecrypt(cipherText []byte) ([]byte, error) {
        block, _ := pem.Decode(privateKey)
        if block == nil {
            return nil, errors.New("private key error!")
        }
        priv, err := x509.ParsePKCS1PrivateKey(block.Bytes)
        if err != nil {
            return nil, err
        }

        return rsa.DecryptPKCS1v15(rand.Reader, priv, cipherText)
    }

now you get the encrypted text originText reference from

https://segmentfault./q/1010000002505932

4: Further more, you can generate key pair in go

func GenRsaKey(bits int) error {
    privateKey, err := rsa.GenerateKey(rand.Reader, bits)
    if err != nil {
        return err
    }
    derStream := x509.MarshalPKCS1PrivateKey(privateKey)
    block := &pem.Block{
        Type:  "privete key",
        Bytes: derStream,
    }
    file, err := os.Create("private.pem")
    if err != nil {
        return err
    }
    err = pem.Encode(file, block)
    if err != nil {
        return err
    }
    publicKey := &privateKey.PublicKey
    derPkix, err := x509.MarshalPKIXPublicKey(publicKey)
    if err != nil {
        return err
    }
    block = &pem.Block{
        Type:  "public key",
        Bytes: derPkix,
    }
    file, err = os.Create("public.pem")
    if err != nil {
        return err
    }
    err = pem.Encode(file, block)
    if err != nil {
        return err
    }
    return nil
}