1 files changed, 136 insertions, 0 deletions
diff --git a/playground/cryptography.go b/playground/cryptography.go
new file mode 100644
index 0000000..6220683
--- /dev/null
+++ b/playground/cryptography.go
@@ -0,0 +1,136 @@
+package main
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/x509"
+	"encoding/asn1"
+	"encoding/base64"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"strings"
+)
+
+const KeyBitSize = 4096
+
+func readFile(filename string) ([]byte, error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return nil, err
+	}
+
+	return ioutil.ReadAll(file)
+}
+
+func writeFile(filename string, data []byte) error {
+	file, err := os.Create(filename)
+	if err != nil {
+		return err
+	}
+
+	_, err = file.Write(data)
+	return err
+}
+
+func signData(data []byte, key *rsa.PublicKey) (string, error) {
+	based := base64.StdEncoding.EncodeToString(data)
+	h := sha256.Sum256([]byte(based))
+	dataHash := fmt.Sprintf("%x", h)
+
+
+	ciphertext, err := rsa.EncryptPKCS1v15(rand.Reader, key, []byte(dataHash))
+	if err != nil {
+		return "", err
+	}
+
+	signature := base64.StdEncoding.EncodeToString(ciphertext)
+	return fmt.Sprintf("%s.%s", based, signature), nil
+}
+
+func checkSignature(signedData string, key *rsa.PrivateKey) (bool, error) {
+	spl := strings.Split(signedData, ".")
+	data := spl[0]
+	signature := spl[1]
+
+	dataHash := fmt.Sprintf("%x", sha256.Sum256([]byte(data)))
+
+	decodedSign, err := base64.StdEncoding.DecodeString(signature)
+	if err != nil {
+		return false, err
+	}
+
+	signHash, err := decodeMessage(decodedSign, key)
+	if err != nil {
+		return false, err
+	}
+
+	return dataHash == string(signHash), nil
+}
+
+func encodeMessage(message []byte, key *rsa.PrivateKey) ([]byte, error) {
+	ciphertext, err := rsa.EncryptPKCS1v15(rand.Reader, &key.PublicKey, message)
+	if err != nil {
+		return nil, err
+	}
+	return ciphertext, nil
+}
+
+func decodeMessage(ciphertext []byte, key *rsa.PrivateKey) ([]byte, error) {
+	plaintext, err := rsa.DecryptPKCS1v15(rand.Reader, key, ciphertext)
+	if err != nil { return nil, err }
+	return plaintext, nil
+}
+
+func loadPublicPEM(filename string) (*rsa.PublicKey, error) {
+	pemBytes, err := readFile(filename)
+	if err != nil {
+		return nil, err
+	}
+
+	block, _ := pem.Decode(pemBytes)
+	if block == nil {
+		return nil, errors.New("there is no key in file")
+	}
+
+	return x509.ParsePKCS1PublicKey(block.Bytes)
+}
+
+func loadPrivatePEM(filename string) (*rsa.PrivateKey, error) {
+	pemBytes, err := readFile(filename)
+	if err != nil {
+		return nil, err
+	}
+
+	block, _ := pem.Decode(pemBytes)
+	if block == nil {
+		return nil, errors.New("there is no key in file")
+	}
+
+	return x509.ParsePKCS1PrivateKey(block.Bytes)
+}
+
+func generateKeys() (keys *rsa.PrivateKey, private []byte, public []byte, err error) {
+	key, err := rsa.GenerateKey(rand.Reader, KeyBitSize)
+	if err != nil {
+		return nil, nil, nil, err
+	}
+
+	var privateKey = &pem.Block{
+		Type: "PRIVATE KEY",
+		Bytes: x509.MarshalPKCS1PrivateKey(key),
+	}
+
+	asn1Bytes, _ := asn1.Marshal(key.PublicKey)
+	var publicKey = &pem.Block{
+		Type: "PUBLIC KEY",
+		Bytes: asn1Bytes,
+	}
+
+	bytePrivate := pem.EncodeToMemory(privateKey)
+	bytePublic := pem.EncodeToMemory(publicKey)
+	return key, bytePrivate, bytePublic, nil
+}