1 files changed, 49 insertions, 0 deletions
diff --git a/http-server/cryptography.go b/http-server/cryptography.go
new file mode 100644
index 0000000..3340446
--- /dev/null
+++ b/http-server/cryptography.go
@@ -0,0 +1,49 @@
+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
+}