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package main
import (
"crypto/rand"
"crypto/rsa"
"crypto/sha256"
"crypto/x509"
"encoding/base64"
"encoding/json"
"encoding/pem"
"errors"
"fmt"
)
func decodeMessage(ciphertext []byte, stringKey string) ([]byte, error) {
block, _ := pem.Decode([]byte(stringKey))
if block == nil {
return nil, errors.New("key is not found in given string")
}
key, err := x509.ParsePKCS1PrivateKey(block.Bytes)
if err != nil {
return nil, err
}
plaintext, err := rsa.DecryptPKCS1v15(rand.Reader, key, ciphertext)
if err != nil {
return nil, err
}
return plaintext, err
}
func checkSignature(req Request, signature string, key string) (bool, error) {
reqBytes, _ := json.Marshal(req)
req64 := base64.StdEncoding.EncodeToString(reqBytes)
h := sha256.Sum256([]byte(req64))
requestHash := fmt.Sprintf("%x", h)
decodedSign, err := base64.StdEncoding.DecodeString(signature)
if err != nil {
return false, err
}
signHash, err := decodeMessage(decodedSign, key)
if err != nil {
return false, err
}
return requestHash == string(signHash), nil
}
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