AES in ECB mode

build.zig

@@ -21,6 +21,8 @@ pub fn build(b: *std.Build) void {
         .target = target,
         .optimize = optimize,
     });
+    exe.linkSystemLibrary2("nettle", .{ .needed = true });
+    exe.linkLibC();
 
     // This declares intent for the executable to be installed into the
     // standard location when the user invokes the "install" step (the default
@@ -55,6 +57,8 @@ pub fn build(b: *std.Build) void {
         .target = target,
         .optimize = optimize,
     });
+    exe_unit_tests.linkSystemLibrary2("nettle", .{ .needed = true });
+    exe_unit_tests.linkLibC();
 
     const run_exe_unit_tests = b.addRunArtifact(exe_unit_tests);
 

src/aes.zig

@@ -0,0 +1,51 @@
+const std = @import("std");
+const nettle = @cImport({
+    @cInclude("nettle/aes.h");
+});
+
+pub const AES = struct {
+    allocator: std.mem.Allocator,
+    key: []const u8,
+    nettle_ctx: nettle.struct_aes_ctx,
+
+    pub fn init(allocator: std.mem.Allocator, key: []const u8) AES {
+        const owned_key = allocator.dupe(u8, key) catch {
+            @panic("Could not allocate key memory");
+        };
+
+        var aes = AES{
+            .allocator = allocator,
+            .key = owned_key,
+            .nettle_ctx = nettle.struct_aes_ctx{},
+        };
+
+        // this works only in this way: first set encrypt then invert for enabling decrypt
+        // this is not commutative
+        nettle.aes_set_encrypt_key(&aes.nettle_ctx, aes.key.len, aes.key.ptr);
+        nettle.aes_invert_key(&aes.nettle_ctx, &aes.nettle_ctx);
+
+        return aes;
+    }
+
+    /// Encrypt buffer `buf`. Must be integer multiple of keysize.
+    /// Caller must free result.
+    pub fn encrypt(self: @This(), allocator: std.mem.Allocator, buf: []const u8) ![]u8 {
+        const enc = try allocator.alloc(u8, buf.len);
+
+        nettle.aes_encrypt(&self.nettle_ctx, buf.len, enc.ptr, buf.ptr);
+        return enc;
+    }
+
+    /// Decrypt buffer `buf`. Must be integer multiple of keysize.
+    /// Caller must free result.
+    pub fn decrypt(self: @This(), allocator: std.mem.Allocator, buf: []const u8) ![]u8 {
+        const dec = try allocator.alloc(u8, buf.len);
+
+        nettle.aes_decrypt(&self.nettle_ctx, buf.len, dec.ptr, buf.ptr);
+        return dec;
+    }
+
+    pub fn deinit(self: @This()) void {
+        self.allocator.free(self.key);
+    }
+};

src/main.zig

@@ -3,6 +3,7 @@ const b64 = @import("base64.zig");
 const hex = @import("hex.zig");
 const xor = @import("xor.zig");
 const xor_crack = @import("xor_crack.zig");
+const aes = @import("aes.zig");
 
 pub fn main() !void {
     var gpa = std.heap.GeneralPurposeAllocator(.{}){};
@@ -36,6 +37,10 @@ pub fn main() !void {
     if (std.mem.eql(u8, args[1], "s1c6")) {
         try s1c6(allocator, stdout);
     }
+
+    if (std.mem.eql(u8, args[1], "s1c7")) {
+        try s1c7(allocator, stdout);
+    }
 }
 
 fn s1c1(allocator: std.mem.Allocator, stdout: anytype) !void {
@@ -178,3 +183,35 @@ fn s1c6(allocator: std.mem.Allocator, stdout: anytype) !void {
 
     try stdout.print("{s}", .{result});
 }
+
+fn s1c7(allocator: std.mem.Allocator, stdout: anytype) !void {
+    // prepare input
+    const f = @embedFile("res/7.txt");
+
+    var f_stream = std.io.fixedBufferStream(f);
+    const reader = f_stream.reader();
+
+    var joined_lines = std.ArrayList(u8).init(allocator);
+    defer joined_lines.deinit();
+    const joined_lines_writer = joined_lines.writer();
+
+    while (true) {
+        reader.streamUntilDelimiter(joined_lines_writer, '\n', null) catch |err| {
+            if (err == error.EndOfStream) break else return err;
+        };
+    }
+
+    const input_decoded = try b64.decode(allocator, joined_lines.items);
+    defer allocator.free(input_decoded);
+
+    // decrypt
+    const key = "YELLOW SUBMARINE";
+
+    const cipher = aes.AES.init(allocator, key);
+    defer cipher.deinit();
+
+    const result = try cipher.decrypt(allocator, input_decoded);
+    defer allocator.free(result);
+
+    try stdout.print("{s}", .{result});
+}

src/res/7.txt

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