shreyner · February 7, 2023 13:48 · Nov 17, 2022 · Jan 23, 2020 · Jan 23, 2020 · Jan 23, 2020
diff --git a/cipherstreams.go b/cipherstreams.go
@@ -106,7 +106,7 @@ func main() {
 	w, _ = EncryptedWriter(secretKey, file)
 	io.WriteString(w, "Hello again gophers!")
 
-	file, _ = os.Open("/tmp/encmsg.txt")
+	file, _ = os.Open("/tmp/encmsg.txt") // use flags/file param for prod code
 	r, _ = EncryptedReader(secretKey, file)
 	contents, _ := ioutil.ReadAll(r)
 	fmt.Printf("contents of decrypted file = %s\n", contents)

diff --git a/cipherstreams.go b/cipherstreams.go
@@ -15,10 +15,6 @@ import (
 
 // EncryptedWriter wraps w with an OFB cipher stream.
 func EncryptedWriter(key string, w io.Writer) (*cipher.StreamWriter, error) {
-	block, err := newBlock(key)
-	if err != nil {
-		return nil, err
-	}
 
 	// generate random initial value
 	iv := make([]byte, aes.BlockSize)
@@ -32,16 +28,17 @@ func EncryptedWriter(key string, w io.Writer) (*cipher.StreamWriter, error) {
 		return nil, errors.New("could not write initial value")
 	}
 
+	block, err := newBlock(key)
+	if err != nil {
+		return nil, err
+	}
+
 	stream := cipher.NewOFB(block, iv)
 	return &cipher.StreamWriter{S: stream, W: w}, nil
 }
 
 // EncryptedReader wraps r with an OFB cipher stream.
 func EncryptedReader(key string, r io.Reader) (*cipher.StreamReader, error) {
-	block, err := newBlock(key)
-	if err != nil {
-		return nil, err
-	}
 
 	// read initial value
 	iv := make([]byte, aes.BlockSize)
@@ -50,6 +47,11 @@ func EncryptedReader(key string, r io.Reader) (*cipher.StreamReader, error) {
 		return nil, errors.New("could not read initial value")
 	}
 
+	block, err := newBlock(key)
+	if err != nil {
+		return nil, err
+	}
+
 	stream := cipher.NewOFB(block, iv)
 	return &cipher.StreamReader{S: stream, R: r}, nil
 }

diff --git a/main.go → cipherstreams.go b/main.go → cipherstreams.go
diff --git a/main.go b/main.go
@@ -0,0 +1,111 @@
+package main
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/md5"
+	"crypto/rand"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"strings"
+)
+
+// EncryptedWriter wraps w with an OFB cipher stream.
+func EncryptedWriter(key string, w io.Writer) (*cipher.StreamWriter, error) {
+	block, err := newBlock(key)
+	if err != nil {
+		return nil, err
+	}
+
+	// generate random initial value
+	iv := make([]byte, aes.BlockSize)
+	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
+		return nil, err
+	}
+
+	// write clear IV to allow for decryption
+	n, err := w.Write(iv)
+	if err != nil || n != len(iv) {
+		return nil, errors.New("could not write initial value")
+	}
+
+	stream := cipher.NewOFB(block, iv)
+	return &cipher.StreamWriter{S: stream, W: w}, nil
+}
+
+// EncryptedReader wraps r with an OFB cipher stream.
+func EncryptedReader(key string, r io.Reader) (*cipher.StreamReader, error) {
+	block, err := newBlock(key)
+	if err != nil {
+		return nil, err
+	}
+
+	// read initial value
+	iv := make([]byte, aes.BlockSize)
+	n, err := r.Read(iv)
+	if err != nil || n != len(iv) {
+		return nil, errors.New("could not read initial value")
+	}
+
+	stream := cipher.NewOFB(block, iv)
+	return &cipher.StreamReader{S: stream, R: r}, nil
+}
+
+func newBlock(key string) (cipher.Block, error) {
+	hash := md5.Sum([]byte(key))
+	block, err := aes.NewCipher(hash[:])
+	if err != nil {
+		return nil, err
+	}
+	return block, nil
+}
+
+func main() {
+
+	// Load your secret key from a safe
+	// place and use for encrypt/decrypt
+	secretKey := "1234567890abcdefghijk"
+
+	/******************************************/
+	/* example to encrypt/decrypt to a string */
+	/******************************************/
+	var sb strings.Builder
+	w, err := EncryptedWriter(secretKey, &sb)
+	if err != nil {
+		panic(err)
+	}
+
+	// as w is a StreamWriter we can write/encrypt directly to it
+	w.Write([]byte("Hello gophers!"))
+	encrypted := sb.String()
+	fmt.Printf("encrypted message = %s\n", encrypted)
+
+	// as r is a StreamReader we can decrypt/read directly from it
+	r, err := EncryptedReader(secretKey, strings.NewReader(encrypted))
+	if err != nil {
+		panic(err)
+	}
+
+	decrypted, _ := ioutil.ReadAll(r)
+	fmt.Printf("decrypted message = %s\n", decrypted)
+
+	/*********************************************************/
+	/* example to encrypt/decrypt to a file                  */
+	/* skipping error handling and file.Close() for examples */
+	/*********************************************************/
+	file, err := os.Create("/tmp/encmsg.txt")
+	if err != nil {
+		panic(err)
+	}
+
+	w, _ = EncryptedWriter(secretKey, file)
+	io.WriteString(w, "Hello again gophers!")
+
+	file, _ = os.Open("/tmp/encmsg.txt")
+	r, _ = EncryptedReader(secretKey, file)
+	contents, _ := ioutil.ReadAll(r)
+	fmt.Printf("contents of decrypted file = %s\n", contents)
+}
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