diff --git a/src/crypto/hkdf.zig b/src/crypto/hkdf.zig
index f1e9458..05a93a8 100644
--- a/src/crypto/hkdf.zig
+++ b/src/crypto/hkdf.zig
@@ -1,9 +1,29 @@
 pub const Implementation = struct {
     
+     prk_length: comptime_int,
+
+     expand: *const fn (out: []u8, ctx: []const u8, prk: *[Implementation.prk_length]u8) void,
+     extract: *const fn (out: *[Implementation.prk_length]u8, salt: []const u8, ikm: []const u8) void,
+
 };
 
 pub const defaultImplementation = struct {
     
-    const Hkdf = @import("std").crypto.kdf.hkdf.Hkdf;
+    const Sha256 = @import("std").crypto.hash.sha2.Sha256;
+
+    const HashImpl = Sha256;
+    const HmacImpl = @import("std").crypto.auth.hmac.Hmac(HashImpl);
+
+    const Hkdf = @import("std").crypto.kdf.hkdf.Hkdf(HmacImpl);
+
+    pub const prk_length = Hkdf.prk_length;
+
+    pub fn expand(out: []u8, ctx: []const u8, prk: *[prk_length]u8) void {
+        Hkdf.expand(out, ctx, prk);
+    }
+
+    pub fn extract(out: *[prk_length]u8, salt: []const u8, ikm: []const u8) void {
+        out *= Hkdf.extract(salt, ikm);
+    }
 
 };
diff --git a/src/crypto/hmac.zig b/src/crypto/hmac.zig
index cb096e8..131bb20 100644
--- a/src/crypto/hmac.zig
+++ b/src/crypto/hmac.zig
@@ -1,15 +1,20 @@
 pub const Implementation = struct {
     
+    mac_length: comptime_int,
+    
+    create: *const fn (out: *[Implementation.mac_length]u8, msg: []const u8, key: []const u8) void,
 };
 
 pub const defaultImplementation = struct {
     
-    const Hmac = @import("std").crypto.auth.hmac.Hmac;
+    const Sha256 = @import("std").crypto.hash.sha2.Sha256;
 
-    pub fn create(out: []u8, msg: []const u8, key: []const u8) !void {
-        _ = out;
-        _ = msg;
-        _ = key;
-        return error.NotImplemented;
+    const HashImpl = Sha256;
+    const Hmac = @import("std").crypto.auth.hmac.Hmac(Sha256);
+
+    pub const mac_length = Hmac.mac_length;
+
+    pub fn create(out: *[mac_length]u8, msg: []const u8, key: []const u8) void {
+        Hmac.create(out, msg, key);
     }
 };
diff --git a/src/crypto/sha256.zig b/src/crypto/sha256.zig
index 70478e0..0d913a1 100644
--- a/src/crypto/sha256.zig
+++ b/src/crypto/sha256.zig
@@ -1,18 +1,17 @@
 pub const Implementation = struct {
     
-    hash: *const fn (buffer: []const u8, out: []u8) void,
+    hash_length: comptime_int,
+
+    hash: *const fn (buffer: []const u8, out: *[Implementation.hash_length]u8) void,
 };
 
 pub const defaultImplementation = struct {
     
     const Sha256 = @import("std").crypto.hash.sha2.Sha256;
 
-    const HASH_LEN = 32; // In bytes
+    pub const hash_len = Sha256.digest_length;
 
-    pub fn hash(buffer: []const u8, out: []u8) !void {
-        if (out.len < HASH_LEN) {
-            return error.BufferTooShort;
-        }
+    pub fn hash(buffer: []const u8, out: *[hash_len]u8) !void {
         Sha256.hash(buffer, out, .{});
     }
 };