diff --git a/validity.go b/validity.go
new file mode 100644
index 0000000..c398021
--- /dev/null
+++ b/validity.go
@@ -0,0 +1,67 @@
+package micha
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"errors"
+	"fmt"
+	"net/url"
+	"sort"
+	"strings"
+)
+
+var (
+	ErrInvalidHash = errors.New("invalid hash")
+)
+
+// ValidateAuthCallback - https://core.telegram.org/widgets/login#checking-authorization
+func ValidateAuthCallback(values url.Values, botToken string) error {
+	secret := sha256.Sum256([]byte(botToken))
+
+	return validateHash(values, secret[:])
+}
+
+// ValidateWabAppData - https://core.telegram.org/bots/webapps#validating-data-received-via-the-mini-app
+func ValidateWabAppData(values url.Values, botToken string) error {
+	hm := hmac.New(sha256.New, []byte("WebAppData"))
+	_, err := hm.Write([]byte(botToken))
+	if err != nil {
+		return err
+	}
+
+	secret := hm.Sum(nil)
+
+	return validateHash(values, secret)
+}
+
+func validateHash(values url.Values, secret []byte) error {
+	hm := hmac.New(sha256.New, secret)
+	_, err := hm.Write([]byte(buildCheckString(values)))
+	if err != nil {
+		return err
+	}
+
+	if fmt.Sprintf("%x", hm.Sum(nil)) != values.Get("hash") {
+		return ErrInvalidHash
+	}
+
+	return nil
+}
+
+func buildCheckString(values url.Values) string {
+	keys := []string{}
+	for key := range values {
+		if key == "hash" {
+			continue
+		}
+		keys = append(keys, key)
+	}
+
+	sort.Strings(keys)
+	parts := []string{}
+	for _, key := range keys {
+		parts = append(parts, fmt.Sprintf("%s=%s", key, values.Get(key)))
+	}
+
+	return strings.Join(parts, "\n")
+}
diff --git a/validity_test.go b/validity_test.go
new file mode 100644
index 0000000..ca799a6
--- /dev/null
+++ b/validity_test.go
@@ -0,0 +1,43 @@
+package micha
+
+import (
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestBuildCheckString(t *testing.T) {
+	values := url.Values{
+		"id":         {"12807202"},
+		"first_name": {"John"},
+		"username":   {"doe"},
+		"photo_url":  {"https://t.me/i/userpic/320/a4f15041-e6a3-4cf4-9363-b0cba2f66720.jpg"},
+		"auth_date":  {"1722489598"},
+		"hash":       {"a19016198a35deb3469a2af3c5aa1f40aa71941cf14cc20e7be8c6507b147061"},
+	}
+
+	require.Equal(t,
+		"auth_date=1722489598\nfirst_name=John\nid=12807202\nphoto_url=https://t.me/i/userpic/320/a4f15041-e6a3-4cf4-9363-b0cba2f66720.jpg\nusername=doe",
+		buildCheckString(values),
+	)
+}
+
+func TestValidateHash(t *testing.T) {
+	values := url.Values{
+		"id":         {"12807202"},
+		"first_name": {"John"},
+		"username":   {"doe"},
+		"photo_url":  {"https://t.me/i/userpic/320/a4f15041-e6a3-4cf4-9363-b0cba2f66720.jpg"},
+		"auth_date":  {"1722489598"},
+		"hash":       {"aba23cb08c508bd952abb2a9b3c2e9b3d6a2c8726145ccea53bd660d7995b586"},
+	}
+
+	// Test valid
+	err := validateHash(values, []byte("111"))
+	require.Nil(t, err)
+
+	// Test invalid
+	err = validateHash(values, []byte("222"))
+	require.NotNil(t, err)
+}