Added decrypt

src/main.zig

@@ -12,9 +12,46 @@ pub fn main() !void {
 
     try crypto.pwhash.argon2.kdf(allocator, &key, pwd, &nonce, crypto.pwhash.argon2.Params.interactive_2id, crypto.pwhash.argon2.Mode.argon2id);
     try encrypt("test.txt", key, nonce);
+    try decrypt(allocator, "test.txt.cha", pwd[0..]);
+}
+
+pub fn decrypt(allocator: std.mem.Allocator, path: []const u8, pwd: []const u8) !void {
+    {
+        var out_buf: [512]u8 = undefined;
+        var in_buf: [512]u8 = undefined;
+        var nonce: [24]u8 = undefined;
+        var key: [32]u8 = undefined;
+
+        var file = try std.fs.cwd().openFile(path, .{});
+        defer file.close();
+
+        _ = try file.read(&nonce);
+
+        try crypto.pwhash.argon2.kdf(allocator, &key, pwd, &nonce, crypto.pwhash.argon2.Params.interactive_2id, crypto.pwhash.argon2.Mode.argon2id);
+        var out_file = try std.fs.cwd().createFile(path[0 .. path.len - 4], .{
+            .read = true,
+            .truncate = true,
+        });
+        defer out_file.close();
+
+        var counter: u32 = 0;
+        var read: usize = 0;
+        while (true) {
+            read = try file.read(&in_buf);
+            if (read <= 0) {
+                break;
+            }
+
+            crypto.stream.chacha.XChaCha20IETF.xor(out_buf[0..read], in_buf[0..read], counter, key, nonce);
+            counter += 1;
+            _ = try out_file.write(out_buf[0..read]);
+        }
+    }
+    try std.fs.cwd().deleteFile(path);
 }
 
 pub fn encrypt(path: []const u8, key: [32]u8, nonce: [24]u8) !void {
+    {
         var file = try std.fs.cwd().openFile(path, .{});
         defer file.close();
         var out_buf: [512]u8 = undefined;
@@ -41,4 +78,6 @@ pub fn encrypt(path: []const u8, key: [32]u8, nonce: [24]u8) !void {
             counter += 1;
             _ = try out_file.write(out_buf[0..read]);
         }
+    }
+    try std.fs.cwd().deleteFile(path);
 }