diff --git a/data/data.go b/data/data.go
new file mode 100644
index 0000000..ec7fb2c
--- /dev/null
+++ b/data/data.go
@@ -0,0 +1,83 @@
+// Package data provides utilities for interacting with database data
+// throughout Write.as.
+package data
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"errors"
+	"fmt"
+)
+
+// Encryption parameters
+const (
+	keyLen    = 32
+	delimiter = '%'
+)
+
+// Encrypt AES-encrypts given text with the given key k.
+// This is used for encrypting sensitive information in the database, such as
+// oAuth tokens and email addresses.
+func Encrypt(k []byte, text string) ([]byte, error) {
+	// Validate parameters
+	if len(k) != keyLen {
+		return nil, errors.New(fmt.Sprintf("Invalid key length (must be %d bytes).", keyLen))
+	}
+
+	// Encrypt plaintext with AES-GCM
+	block, err := aes.NewCipher(k)
+	if err != nil {
+		return nil, err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+
+	// Generate nonce
+	ns := gcm.NonceSize()
+	nonce := make([]byte, ns)
+	if _, err := rand.Read(nonce); err != nil {
+		return nil, err
+	}
+
+	ciphertext := gcm.Seal(nil, nonce, []byte(text), nil)
+
+	// Build text output in the format:
+	// NonceCiphertext
+	outtext := append(nonce, ciphertext...)
+
+	return outtext, nil
+}
+
+// Decrypt decrypts the given ciphertext with the given key k.
+func Decrypt(k, ciphertext []byte) ([]byte, error) {
+	// Decrypt ciphertext
+	block, err := aes.NewCipher(k)
+	if err != nil {
+		return nil, err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+
+	ns := gcm.NonceSize()
+
+	// Validate data
+	if len(ciphertext) < ns {
+		return nil, errors.New("Ciphertext is too short")
+	}
+
+	nonce := ciphertext[:ns]
+	ciphertext = ciphertext[ns:]
+	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	return plaintext, nil
+}
diff --git a/data/data_test.go b/data/data_test.go
new file mode 100644
index 0000000..33dbc04
--- /dev/null
+++ b/data/data_test.go
@@ -0,0 +1,70 @@
+// Package data provides utilities for interacting with database data
+// throughout Write.as.
+package data
+
+import (
+	"bytes"
+	"crypto/rand"
+	"strings"
+	"testing"
+)
+
+func TestEncDec(t *testing.T) {
+	// Generate a random key with a valid length
+	k := make([]byte, keyLen)
+	_, err := rand.Read(k)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	runEncDec(t, k, "this is my secret message™. 😄", nil)
+	runEncDec(t, k, "mygreatemailaddress@gmail.com", nil)
+}
+
+func TestAuthentication(t *testing.T) {
+	// Generate a random key with a valid length
+	k := make([]byte, keyLen)
+	_, err := rand.Read(k)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	runEncDec(t, k, "mygreatemailaddress@gmail.com", func(c []byte) []byte {
+		c[0] = 'a'
+		t.Logf("Modified:   %s\n", c)
+		return c
+	})
+}
+
+func runEncDec(t *testing.T, k []byte, plaintext string, transform func([]byte) []byte) {
+	t.Logf("Plaintext:  %s\n", plaintext)
+
+	// Encrypt the data
+	ciphertext, err := Encrypt(k, plaintext)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Logf("Ciphertext: %s\n", ciphertext)
+
+	if transform != nil {
+		ciphertext = transform(ciphertext)
+	}
+
+	// Decrypt the data
+	decryptedText, err := Decrypt(k, ciphertext)
+	if err != nil {
+		if transform != nil && strings.Contains(err.Error(), "message authentication failed") {
+			// We modified the ciphertext; make sure we're getting the right error
+			t.Logf("%v\n", err)
+			return
+		}
+		t.Fatal(err)
+	}
+
+	t.Logf("Decrypted:  %s\n", string(decryptedText))
+
+	if !bytes.Equal([]byte(plaintext), decryptedText) {
+		t.Errorf("Plaintext mismatch: got %x vs %x", plaintext, decryptedText)
+	}
+}