Reputation: 41

Use Go to encrypt message with ssh-rsa public key which then can be decrypted using openssl rsautl -decrypt

I have been trying to solve this for days. In Go code I am looking to take a ssh-rsa public key like:

ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDGnnY4LuLq7Bs7VnFk2Vs6hNTmZLkUBRRhXNFyKZOCvmhKcM7BSHkGS7+phpIzj6mTOsJEBZKHQgac46COOT3ukO/farnnDz78KIq24U/+TZmyAyNNdzOVizK5aAApvpYTQpuSlIDDltLXQkPokedE/5vCIPiwVZW0TfqT/Rdy2XXwKewDQ05xvJhX3+nymZkyJX3GJ+pTfsDkKR+suSLDN3nupThPiWK5A1ZG9bbUkxHbsAXiTKS+qwADIWOtJvfNtPX54JjCo3Gh3/Fy0Ovxn3QSQlCF/IZNbSgm6R6adjaU4kXEF6zsLq+BjDKLtEA3A0tAIBj0T+DuuxpcV3aX

and message like: hello-world and encrypt that message with that key.

The private key is then going to be used to decrypt the key with openssl rsautl -decrypt -inkey privateKeyFile -in encryptedMsgFile

Upvotes: 4

Answers (1)

Topaco

Reputation: 49241

Encryption with SSH keys is described in detail in the post Encrypting Data With SSH Keys and Golang, in particular the import of the OpenSSH public key, for which the ssh package is applied. For encryption (with PKCS#1 v1.5 padding) the rsa package is used.

The following sample code illustrates this. Since the OpenSSL statement reads the ciphertext from a file, it makes most sense for the ciphertext to be stored in a binary file. For simplicity, however, in this example the cipher text is output hex encoded:

package main

import (
    "crypto/rand"
    "crypto/rsa"
    "encoding/hex"
    "fmt"

    "golang.org/x/crypto/ssh"
)

func main() {

    // Key import
    publicKey := "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC8NGcNWf6cUno2lpny36js9ynXCQ6kuJ14yIViuPwty0ZkfhpPdw3zVKWmKV0zS1/QyO6a5d85I9ywvEXHiZr4+fE4JRPxdEIQVGMz7OThs0XgluE4zZrw55ywMt/b6elPC2TkshUHQfDYQuIh1ZBqFOnvUIh8yyGc1L4sLACGY75tpvSE29RZQRmaZaV5YpzIM0SbpFirOqWsjKd3kLMjPqPr9+ISpqOP2tTfOfw9IW8gvRUYa2oRUEyE7Ju4QrwSWmKj9JK9KTeAzRiy5rsSW6issDaxQIYg2BNT8YLrNVm+FWpOVRud6KwohOpk8/YeM0EKEO3vAfGJH6tYT9Zv whatever"
    parsed, _, _, _, err := ssh.ParseAuthorizedKey([]byte(publicKey))
    if err != nil {
        panic(err)
    }
    parsedCryptoKey := parsed.(ssh.CryptoPublicKey)
    pubCrypto := parsedCryptoKey.CryptoPublicKey()
    pub := pubCrypto.(*rsa.PublicKey)

    // Encryption
    msg := "The quick brown fox jumps over the lazy dog"
    encryptedBytes, err := rsa.EncryptPKCS1v15(
        rand.Reader,
        pub,
        []byte(msg),
    )
    if err != nil {
        panic(err)
    }
    fmt.Println(hex.EncodeToString(encryptedBytes))
}

A possible hex encoded ciphertext is:

7610da88661fc80b145f3bdd415cb71e73b1ad5100f7b5a9d9c5d27d9e3645d626dd784ccc5cc6c1e44aeec04b0e64072bfe1b58e88feec4b5e6ca63a14c5a23dad1370a303f2f775f4e6f349bab52a3f5883a51ac1f53247a4e05fb9989fc999878ac8f3821da0a079272738145dda7a340b7e4d44d922e563558972444b6f7400a4affffe2a6ee42d400cff51bf3eecc8cd1ffc9ea8c8d04ff6ef0e566d105a4841bcece7b16e2068a321e0c7b4cb964593fcf59795f0a14ec1ac95b941eaa452912bca2e1431992672dcdcc1ea42ff956ef7d21f126a1650c4a306817b4e094ee8c50a01dcc04a7be25e0c01b2ba678be3561774ae859353b5cc98a3b9b11

Note that this encryption is not deterministic, i.e. when you execute the code, you will get a different ciphertext.

Decryption is possible with the posted OpenSSL statement:

openssl rsautl -decrypt -inkey privateKeyFile -in encryptedMsgFile

taking into account:

encryptedMsgFile contains the binary data of the ciphertext, i.e. the hex decoding of 7610da... (if the ciphertext is stored directly as a binary file as mentioned above, encryptedMsgFile would correspond to this file).

privateKeyFile contains the PEM encoded private PKCS#1 or PKCS#8 key. If your key is in OpenSSH's proprietary format (-----BEGIN OPENSSH PRIVATE KEY-----...), it must be converted to e.g. PKCS#8 format, e.g. with ssh_keygen:

ssh-keygen -p -N "" -m pkcs8 -f data.key

Note that data.key contains the OpenSSH key and is overwritten with the PKCS#8 key. For the posted example, privateKeyFile is:

Upvotes: 1

Use Go to encrypt message with ssh-rsa public key which then can be decrypted using openssl rsautl -decrypt

Answers (1)

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