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Example of RSA encryption, decryption, signing, and verification in Go
package main
import (
"crypto"
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"encoding/base64"
"fmt"
)
func main() {
// The GenerateKey method takes in a reader that returns random bits, and
// the number of bits
privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
if err != nil {
panic(err)
}
// The public key is a part of the *rsa.PrivateKey struct
publicKey := privateKey.PublicKey
// use the public and private keys
// ...
// https://play.golang.org/p/tldFUt2c4nx
modulusBytes := base64.StdEncoding.EncodeToString(privateKey.N.Bytes())
privateExponentBytes := base64.StdEncoding.EncodeToString(privateKey.D.Bytes())
fmt.Println(modulusBytes)
fmt.Println(privateExponentBytes)
fmt.Println(publicKey.E)
encryptedBytes, err := rsa.EncryptOAEP(
sha256.New(),
rand.Reader,
&publicKey,
[]byte("super secret message"),
nil)
if err != nil {
panic(err)
}
fmt.Println("encrypted bytes: ", encryptedBytes)
// The first argument is an optional random data generator (the rand.Reader we used before)
// we can set this value as nil
// The OEAPOptions in the end signify that we encrypted the data using OEAP, and that we used
// SHA256 to hash the input.
decryptedBytes, err := privateKey.Decrypt(nil, encryptedBytes, &rsa.OAEPOptions{Hash: crypto.SHA256})
if err != nil {
panic(err)
}
// We get back the original information in the form of bytes, which we
// the cast to a string and print
fmt.Println("decrypted message: ", string(decryptedBytes))
msg := []byte("verifiable message")
// Before signing, we need to hash our message
// The hash is what we actually sign
msgHash := sha256.New()
_, err = msgHash.Write(msg)
if err != nil {
panic(err)
}
msgHashSum := msgHash.Sum(nil)
// In order to generate the signature, we provide a random number generator,
// our private key, the hashing algorithm that we used, and the hash sum
// of our message
signature, err := rsa.SignPSS(rand.Reader, privateKey, crypto.SHA256, msgHashSum, nil)
if err != nil {
panic(err)
}
// To verify the signature, we provide the public key, the hashing algorithm
// the hash sum of our message and the signature we generated previously
// there is an optional "options" parameter which can omit for now
err = rsa.VerifyPSS(&publicKey, crypto.SHA256, msgHashSum, signature, nil)
if err != nil {
fmt.Println("could not verify signature: ", err)
return
}
// If we don't get any error from the `VerifyPSS` method, that means our
// signature is valid
fmt.Println("signature verified")
}
@fX4N1DmH311X39SpxXLWxMWy49n6o8zb
package main

import (
    "crypto/rand"
    "crypto/rsa"
    "crypto/x509"
    "encoding/pem"
    "errors"
    "fmt"
)

func GenerateRsaKeyPair() (*rsa.PrivateKey, *rsa.PublicKey) {
    privkey, _ := rsa.GenerateKey(rand.Reader, 4096)
    return privkey, &privkey.PublicKey
}

func ExportRsaPrivateKeyAsPemStr(privkey *rsa.PrivateKey) string {
    privkey_bytes := x509.MarshalPKCS1PrivateKey(privkey)
    privkey_pem := pem.EncodeToMemory(
            &pem.Block{
                    Type:  "RSA PRIVATE KEY",
                    Bytes: privkey_bytes,
            },
    )
    return string(privkey_pem)
}

func ParseRsaPrivateKeyFromPemStr(privPEM string) (*rsa.PrivateKey, error) {
    block, _ := pem.Decode([]byte(privPEM))
    if block == nil {
            return nil, errors.New("failed to parse PEM block containing the key")
    }

    priv, err := x509.ParsePKCS1PrivateKey(block.Bytes)
    if err != nil {
            return nil, err
    }

    return priv, nil
}

func ExportRsaPublicKeyAsPemStr(pubkey *rsa.PublicKey) (string, error) {
    pubkey_bytes, err := x509.MarshalPKIXPublicKey(pubkey)
    if err != nil {
            return "", err
    }
    pubkey_pem := pem.EncodeToMemory(
            &pem.Block{
                    Type:  "RSA PUBLIC KEY",
                    Bytes: pubkey_bytes,
            },
    )

    return string(pubkey_pem), nil
}

func ParseRsaPublicKeyFromPemStr(pubPEM string) (*rsa.PublicKey, error) {
    block, _ := pem.Decode([]byte(pubPEM))
    if block == nil {
            return nil, errors.New("failed to parse PEM block containing the key")
    }

    pub, err := x509.ParsePKIXPublicKey(block.Bytes)
    if err != nil {
            return nil, err
    }

    switch pub := pub.(type) {
    case *rsa.PublicKey:
            return pub, nil
    default:
            break // fall through
    }
    return nil, errors.New("Key type is not RSA")
}

func main() {

    // Create the keys
    priv, pub := GenerateRsaKeyPair()

    // Export the keys to pem string
    priv_pem := ExportRsaPrivateKeyAsPemStr(priv)
    pub_pem, _ := ExportRsaPublicKeyAsPemStr(pub)

    // Import the keys from pem string
    priv_parsed, _ := ParseRsaPrivateKeyFromPemStr(priv_pem)
    pub_parsed, _ := ParseRsaPublicKeyFromPemStr(pub_pem)

    // Export the newly imported keys
    priv_parsed_pem := ExportRsaPrivateKeyAsPemStr(priv_parsed)
    pub_parsed_pem, _ := ExportRsaPublicKeyAsPemStr(pub_parsed)

    fmt.Println(priv_parsed_pem)
    fmt.Println(pub_parsed_pem)

    // Check that the exported/imported keys match the original keys
    if priv_pem != priv_parsed_pem || pub_pem != pub_parsed_pem {
            fmt.Println("Failure: Export and Import did not result in same Keys")
    } else {
            fmt.Println("Success")
    }
}

@MarlikAlmighty
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MarlikAlmighty commented Jun 2, 2022

Thank you for the article. But golang doesn't use snake_case, try camelCase.

@fX4N1DmH311X39SpxXLWxMWy49n6o8zb

Thank you for the article. But golang doesn't use snake_case, try camelCase.

IKR,even the function name is exported outside the package scope.

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