Merge pull request 'Cold Storage with One-Way RSA Encryption' (#43) from coldstorage into main

Reviewed-on: #43

.gitignore

@@ -1,5 +1,6 @@
 /nonshy
 /web/static/photos
+/coldstorage
 database.sqlite
 settings.json
 pgdump.sql

cmd/nonshy/main.go

@@ -6,6 +6,7 @@ import (
 
 	nonshy "code.nonshy.com/nonshy/website/pkg"
 	"code.nonshy.com/nonshy/website/pkg/config"
+	"code.nonshy.com/nonshy/website/pkg/encryption/coldstorage"
 	"code.nonshy.com/nonshy/website/pkg/log"
 	"code.nonshy.com/nonshy/website/pkg/models"
 	"code.nonshy.com/nonshy/website/pkg/models/backfill"
@@ -169,6 +170,57 @@ func main() {
 					},
 				},
 			},
+			{
+				Name:  "coldstorage",
+				Usage: "cold storage functions for sensitive files",
+				Subcommands: []*cli.Command{
+					{
+						Name:  "decrypt",
+						Usage: "decrypt a file from cold storage using the RSA private key",
+						Flags: []cli.Flag{
+							&cli.StringFlag{
+								Name:     "key",
+								Aliases:  []string{"k"},
+								Required: true,
+								Usage:    "RSA private key file for cold storage",
+							},
+							&cli.StringFlag{
+								Name:     "aes",
+								Aliases:  []string{"a"},
+								Required: true,
+								Usage:    "AES key file used with the encrypted item in question (.aes file)",
+							},
+							&cli.StringFlag{
+								Name:     "input",
+								Aliases:  []string{"i"},
+								Required: true,
+								Usage:    "input file to decrypt (.enc file)",
+							},
+							&cli.StringFlag{
+								Name:     "output",
+								Aliases:  []string{"o"},
+								Required: true,
+								Usage:    "output file to write to (like a .jpg file)",
+							},
+						},
+						Action: func(c *cli.Context) error {
+							err := coldstorage.FileFromColdStorage(
+								c.String("key"),
+								c.String("aes"),
+								c.String("input"),
+								c.String("output"),
+							)
+							if err != nil {
+								log.Error("Error decrypting from cold storage: %s", err)
+								return err
+							}
+
+							log.Info("Wrote decrypted file to: %s", c.String("output"))
+							return nil
+						},
+					},
+				},
+			},
 			{
 				Name:  "backfill",
 				Usage: "One-off maintenance tasks and data backfills for database migrations",

docs/Cold Storage.md

@@ -0,0 +1,70 @@
+# Cold Storage
+
+One of the security features of the website is **cold storage** which implements a "one way" encryption process for archiving sensitive files on the site.
+
+The first use case is to archive secondary photo IDs: if a user was requested to provide a scan of their government issued photo ID for approval, the site can archive the original copy to cold storage when approved in case of any future inquiry.
+
+The cold storage feature works by encrypting the file using an RSA public key, and relies on the matching private key to be **removed** from the web server and kept offline; so in case of a hack or data breach, the key that can decrypt the cold storage files will **NOT** be kept on the same web server.
+
+This document explains how this feature works and how to configure it.
+
+## Initialization
+
+When the server starts up and there is not a cold storage RSA key configured, the feature will be initialized by generating new RSA encryption keys:
+
+* The directory `./coldstorage/keys` is created and the RSA keys will be written in files named **private.pem** and **public.pem**.
+* The RSA public key is _also_ written into the **settings.json** file for the server, at the Encryption / ColdStorageRSAPublicKey property.
+
+You should **move the keys OFF of your web server machine** and keep them safe for your bookkeeping. Notably, the `private.pem` key is the sensitive file that should be removed.
+
+The app does not need either of these keys to remain on the server: the settings.json has a copy of the RSA public key which the app uses to create cold storage encrypted files.
+
+### Admin Dashboard Warning
+
+As a safety precaution: if the private.pem key remains on disk, a warning is shown at the top of the Admin Dashboard page of the website to remind you that the key should be removed and stored safely offline.
+
+## Recovering from Cold Storage
+
+Should you need to recover an encrypted file from cold storage, the `nonshy coldstorage decrypt` command built into the Go server binary has the function to decrypt the files.
+
+Every item that is moved into cold storage generates two files: an encrypted AES key file (`.aes`) and the encrypted data file itself (with a `.enc` extension). For example, a "photo.jpg" might go into cold storage as two files: "photo.jpg.aes" and "photo.jpg.enc"
+
+You will need the following three files to decrypt from cold storage:
+
+1. The RSA private key file (private.pem)
+2. The encrypted AES key file (.aes extension)
+3. The encrypted cold storage data file (.enc extension)
+
+The command to decrypt them is thus like:
+
+```bash
+# command example
+nonshy coldstorage decrypt \
+    --key private.pem \
+    --aes photo.jpg.aes \
+    --input photo.jpg.enc \
+    --output photo.jpg
+
+# short command line flags work too
+nonshy coldstorage decrypt -k private.pem \
+    -a photo.jpg.aes -i photo.jpg.enc \
+    -o photo.jpg
+```
+
+The `--output` file is where the decrypted file will be written to.
+
+## Encryption Algorithms
+
+When a file is moved into cold storage:
+
+1. A fresh new AES symmetric key is generated from scratch.
+2. The AES key is encrypted using the **RSA public key** and written to the ".aes" file in the coldstorage/ folder.
+3. The original file is encrypted using that AES symmetric key and written to the ".enc" file in the coldstorage/ folder.
+
+At the end of the encrypt function: the web server no longer has the AES key and is _unable_ to decrypt it because the private key is not available (as it should be kept offline for security).
+
+Decrypting a file out of cold storage is done like so:
+
+1. The encrypted AES key is unlocked using the **RSA private key**.
+2. The encrypted cold storage file (.enc) is decrypted with that AES key.
+3. The cleartext data is written to the output file.

pkg/config/variable.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"os"
 
+	"code.nonshy.com/nonshy/website/pkg/encryption/coldstorage"
 	"code.nonshy.com/nonshy/website/pkg/encryption/keygen"
 	"code.nonshy.com/nonshy/website/pkg/log"
 	"github.com/google/uuid"
@@ -13,7 +14,7 @@ import (
 
 // Version of the config format - when new fields are added, it will attempt
 // to write the settings.toml to disk so new defaults populate.
-var currentVersion = 3
+var currentVersion = 4
 
 // Current loaded settings.json
 var Current = DefaultVariable()
@@ -97,6 +98,19 @@ func LoadSettings() {
 		writeSettings = true
 	}
 
+	// Initialize the cold storage RSA keys.
+	if len(Current.Encryption.ColdStorageRSAPublicKey) == 0 {
+		x509publicKey, err := coldstorage.Initialize()
+		if err != nil {
+			log.Error("Initializing cold storage: %s", err)
+			os.Exit(1)
+		}
+
+		// Store the public key in the settings.json.
+		Current.Encryption.ColdStorageRSAPublicKey = x509publicKey
+		writeSettings = true
+	}
+
 	// Have we added new config fields? Save the settings.json.
 	if Current.Version != currentVersion || writeSettings {
 		log.Warn("New options are available for your settings.json file. Your settings will be re-saved now.")
@@ -164,6 +178,7 @@ type Maintenance struct {
 // Encryption settings.
 type Encryption struct {
 	AESKey                  []byte
+	ColdStorageRSAPublicKey []byte
 }
 
 // Turnstile (Cloudflare CAPTCHA) settings.

pkg/controller/admin/dashboard.go

@@ -3,6 +3,7 @@ package admin
 import (
 	"net/http"
 
+	"code.nonshy.com/nonshy/website/pkg/encryption/coldstorage"
 	"code.nonshy.com/nonshy/website/pkg/templates"
 )
 
@@ -10,7 +11,10 @@ import (
 func Dashboard() http.HandlerFunc {
 	tmpl := templates.Must("admin/dashboard.html")
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		if err := tmpl.Execute(w, r, nil); err != nil {
+		var vars = map[string]interface{}{
+			"ColdStorageWarning": coldstorage.Warning(),
+		}
+		if err := tmpl.Execute(w, r, vars); err != nil {
 			http.Error(w, err.Error(), http.StatusInternalServerError)
 			return
 		}

pkg/controller/photo/certification.go

@@ -7,9 +7,11 @@ import (
 	"net/http"
 	"path/filepath"
 	"strconv"
+	"time"
 
 	"code.nonshy.com/nonshy/website/pkg/chat"
 	"code.nonshy.com/nonshy/website/pkg/config"
+	"code.nonshy.com/nonshy/website/pkg/encryption/coldstorage"
 	"code.nonshy.com/nonshy/website/pkg/geoip"
 	"code.nonshy.com/nonshy/website/pkg/log"
 	"code.nonshy.com/nonshy/website/pkg/mail"
@@ -468,6 +470,25 @@ func AdminCertification() http.HandlerFunc {
 
 				// With a secondary photo ID?
 				if cert.SecondaryFilename != "" {
+					// Move the original photo into cold storage.
+					coldStorageFilename := fmt.Sprintf(
+						"photoID-%d-%s-%d.jpg",
+						user.ID,
+						user.Username,
+						time.Now().Unix(),
+					)
+					if err := coldstorage.FileToColdStorage(
+						photo.DiskPath(cert.SecondaryFilename),
+						coldStorageFilename,
+						config.Current.Encryption.ColdStorageRSAPublicKey,
+					); err != nil {
+						session.FlashError(w, r, "Failed to move to cold storage: %s", err)
+						templates.Redirect(w, r.URL.Path)
+						return
+					} else {
+						session.Flash(w, r, "Note: the secondary photo ID was encrypted to cold storage @ %s", coldStorageFilename)
+					}
+
 					// Delete it immediately.
 					if err := photo.Delete(cert.SecondaryFilename); err != nil {
 						session.FlashError(w, r, "Failed to delete old secondary ID cert photo for %s (%s): %s", currentUser.Username, cert.SecondaryFilename, err)

pkg/encryption/coldstorage/coldstorage.go

@@ -0,0 +1,150 @@
+package coldstorage
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"errors"
+	"fmt"
+	"os"
+	"path"
+	"path/filepath"
+
+	"code.nonshy.com/nonshy/website/pkg/encryption/keygen"
+	"code.nonshy.com/nonshy/website/pkg/log"
+)
+
+var (
+	ColdStorageDirectory      = "./coldstorage"
+	ColdStorageKeysDirectory  = path.Join(ColdStorageDirectory, "keys")
+	ColdStoragePrivateKeyFile = path.Join(ColdStorageKeysDirectory, "private.pem")
+	ColdStoragePublicKeyFile  = path.Join(ColdStorageKeysDirectory, "public.pem")
+)
+
+// Initialize generates the RSA key pairs for the first time and creates
+// the cold storage directories. It writes the keys to disk and returns the x509 encoded
+// public key which goes in the settings.json (the keys on disk are for your bookkeeping).
+func Initialize() ([]byte, error) {
+	log.Warn("NOTICE: rolling a random RSA key pair for cold storage")
+	rsaKey, err := keygen.NewRSAKeys()
+	if err != nil {
+		return nil, fmt.Errorf("generate RSA key: %s", err)
+	}
+
+	// Encode to x509
+	x509, err := keygen.SerializePublicKey(rsaKey.Public())
+	if err != nil {
+		return nil, fmt.Errorf("encode RSA public key to x509: %s", err)
+	}
+
+	// Write the public/private key files to disk.
+	if _, err := os.Stat(ColdStorageKeysDirectory); os.IsNotExist(err) {
+		log.Info("Notice: creating cold storage directory")
+		if err := os.MkdirAll(ColdStorageKeysDirectory, 0755); err != nil {
+			return nil, fmt.Errorf("create %s: %s", ColdStorageKeysDirectory, err)
+		}
+	}
+	if err := keygen.WriteRSAKeys(
+		rsaKey,
+		path.Join(ColdStorageKeysDirectory, "private.pem"),
+		path.Join(ColdStorageKeysDirectory, "public.pem"),
+	); err != nil {
+		return nil, fmt.Errorf("export newly generated public/private key files: %s", err)
+	}
+
+	return x509, nil
+}
+
+// Warning returns an error message if the private key is still on disk at its
+// original generated location: it should be moved offline for security.
+func Warning() error {
+	if _, err := os.Stat(ColdStoragePrivateKeyFile); os.IsNotExist(err) {
+		return nil
+	}
+
+	return errors.New("the private key file at ./coldstorage/keys should be moved off of the server and kept offline for safety")
+}
+
+// FileToColdStorage will copy a file, encrypted, into cold storage at the given filename.
+func FileToColdStorage(sourceFilePath, outputFileName string, publicKeyPEM []byte) error {
+	if len(publicKeyPEM) == 0 {
+		return errors.New("no RSA public key")
+	}
+
+	// Load the public key from PEM encoding.
+	publicKey, err := keygen.DeserializePublicKey(publicKeyPEM)
+	if err != nil {
+		return fmt.Errorf("deserializing public key: %s", err)
+	}
+
+	// Generate a unique AES key for encrypting this file in one direction.
+	aesKey, err := keygen.NewAESKey()
+	if err != nil {
+		return err
+	}
+
+	// Encrypt the AES key and store it on disk next to the cold storage file.
+	ciphertext, err := rsa.EncryptPKCS1v15(rand.Reader, publicKey, aesKey)
+	if err != nil {
+		return fmt.Errorf("encrypt error: %s", err)
+	}
+	err = os.WriteFile(
+		filepath.Join(ColdStorageDirectory, outputFileName+".aes"),
+		ciphertext,
+		0600,
+	)
+	if err != nil {
+		return err
+	}
+
+	// Read the original plaintext file going into cold storage.
+	plaintext, err := os.ReadFile(sourceFilePath)
+	if err != nil {
+		return fmt.Errorf("source file: %s", err)
+	}
+
+	// Encrypt the plaintext with the AES key.
+	ciphertext, err = keygen.EncryptWithAESKey(plaintext, aesKey)
+	if err != nil {
+		return err
+	}
+
+	// Write it to disk.
+	return os.WriteFile(filepath.Join(ColdStorageDirectory, outputFileName+".enc"), ciphertext, 0600)
+}
+
+// FileFromColdStorage decrypts a cold storage file and writes it to the output file.
+//
+// The command `nonshy coldstorage decrypt` uses this function. Requirements:
+//
+// - privateKeyFile is the RSA private key originally generated for cold storage
+// - aesKeyFile is the unique .aes file for the cold storage item
+// - ciphertextFile is the encrypted cold storage item
+// - outputFile is where you want to save the result to
+func FileFromColdStorage(privateKeyFile, aesKeyFile, ciphertextFile, outputFile string) error {
+	privateKey, err := keygen.PrivateKeyFromFile(privateKeyFile)
+	if err != nil {
+		return fmt.Errorf("private key file: %s", err)
+	}
+
+	encryptedAESKey, err := os.ReadFile(aesKeyFile)
+	if err != nil {
+		return fmt.Errorf("reading aes key file: %s", err)
+	}
+
+	aesKey, err := rsa.DecryptPKCS1v15(rand.Reader, privateKey, encryptedAESKey)
+	if err != nil {
+		return fmt.Errorf("decrypting the aes key file: %s", err)
+	}
+
+	ciphertext, err := os.ReadFile(ciphertextFile)
+	if err != nil {
+		return fmt.Errorf("reading cold storage file: %s", err)
+	}
+
+	plaintext, err := keygen.DecryptWithAESKey(ciphertext, aesKey)
+	if err != nil {
+		return fmt.Errorf("decrypting cold storage file: %s", err)
+	}
+
+	return os.WriteFile(outputFile, plaintext, 0644)
+}

pkg/encryption/encryption.go

@@ -7,15 +7,12 @@
 package encryption
 
 import (
-	"crypto/aes"
-	"crypto/cipher"
-	"crypto/rand"
 	"crypto/sha256"
 	"errors"
 	"fmt"
-	"io"
 
 	"code.nonshy.com/nonshy/website/pkg/config"
+	"code.nonshy.com/nonshy/website/pkg/encryption/keygen"
 )
 
 // Encrypt a byte stream using the site's AES passphrase.
@@ -24,32 +21,7 @@ func Encrypt(input []byte) ([]byte, error) {
 		return nil, errors.New("AES key not configured")
 	}
 
-	// Generate a new AES cipher.
+	return keygen.EncryptWithAESKey(input, config.Current.Encryption.AESKey)
-	c, err := aes.NewCipher(config.Current.Encryption.AESKey)
-	if err != nil {
-		return nil, err
-	}
-
-	// gcm or Galois/Counter Mode
-	gcm, err := cipher.NewGCM(c)
-	if err != nil {
-		return nil, err
-	}
-
-	// Create a new byte array the size of the GCM nonce
-	// which must be passed to Seal.
-	nonce := make([]byte, gcm.NonceSize())
-	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
-		return nil, fmt.Errorf("populating the nonce: %s", err)
-	}
-
-	// Encrypt the text using the Seal function.
-	// Seal encrypts and authenticates plaintext, authenticates the
-	// additional data and appends the result to dst, returning the
-	// updated slice. The nonce must be NonceSize() bytes long and
-	// unique for all time, for a given key.
-	result := gcm.Seal(nonce, nonce, input, nil)
-	return result, nil
 }
 
 // EncryptString encrypts a string value and returns the cipher text.
@@ -63,27 +35,7 @@ func Decrypt(data []byte) ([]byte, error) {
 		return nil, errors.New("AES key not configured")
 	}
 
-	c, err := aes.NewCipher(config.Current.Encryption.AESKey)
+	return keygen.DecryptWithAESKey(data, config.Current.Encryption.AESKey)
-	if err != nil {
-		return nil, err
-	}
-
-	gcm, err := cipher.NewGCM(c)
-	if err != nil {
-		return nil, err
-	}
-
-	nonceSize := gcm.NonceSize()
-	if len(data) < nonceSize {
-		return nil, errors.New("ciphertext data less than nonceSize")
-	}
-
-	nonce, ciphertext := data[:nonceSize], data[nonceSize:]
-	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
-	if err != nil {
-		return nil, err
-	}
-	return plaintext, nil
 }
 
 // DecryptString decrypts a string value from ciphertext.

pkg/encryption/keygen/aes.go

@@ -0,0 +1,72 @@
+// Package keygen provides the AES key initializer function.
+package keygen
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"errors"
+	"fmt"
+	"io"
+)
+
+// NewAESKey returns a 32-byte (AES 256 bit) encryption key.
+func NewAESKey() ([]byte, error) {
+	var result = make([]byte, 32)
+	_, err := rand.Read(result)
+	return result, err
+}
+
+// EncryptWithAESKey a byte stream using a given AES key.
+func EncryptWithAESKey(input []byte, key []byte) ([]byte, error) {
+	// Generate a new AES cipher.
+	c, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	// gcm or Galois/Counter Mode
+	gcm, err := cipher.NewGCM(c)
+	if err != nil {
+		return nil, err
+	}
+
+	// Create a new byte array the size of the GCM nonce
+	// which must be passed to Seal.
+	nonce := make([]byte, gcm.NonceSize())
+	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
+		return nil, fmt.Errorf("populating the nonce: %s", err)
+	}
+
+	// Encrypt the text using the Seal function.
+	// Seal encrypts and authenticates plaintext, authenticates the
+	// additional data and appends the result to dst, returning the
+	// updated slice. The nonce must be NonceSize() bytes long and
+	// unique for all time, for a given key.
+	result := gcm.Seal(nonce, nonce, input, nil)
+	return result, nil
+}
+
+func DecryptWithAESKey(data []byte, key []byte) ([]byte, error) {
+	c, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	gcm, err := cipher.NewGCM(c)
+	if err != nil {
+		return nil, err
+	}
+
+	nonceSize := gcm.NonceSize()
+	if len(data) < nonceSize {
+		return nil, errors.New("ciphertext data less than nonceSize")
+	}
+
+	nonce, ciphertext := data[:nonceSize], data[nonceSize:]
+	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return nil, err
+	}
+	return plaintext, nil
+}

pkg/encryption/keygen/aes_test.go

@@ -0,0 +1,72 @@
+package keygen_test
+
+import (
+	"testing"
+
+	"code.nonshy.com/nonshy/website/pkg/encryption/keygen"
+)
+
+func TestAES(t *testing.T) {
+	type testCase struct {
+		AESKey    []byte // AES key, nil = generate a new one
+		Input     []byte // input text to encrypt
+		Encrypted []byte // already encrypted text
+		Expect    []byte // expected output on decrypt
+	}
+
+	var tests = []testCase{
+		{
+			Input:  []byte("hello world"),
+			Expect: []byte("hello world"),
+		},
+		{
+			AESKey:    []byte{170, 94, 243, 132, 85, 247, 149, 238, 245, 39, 140, 125, 226, 178, 134, 161, 17, 151, 139, 248, 16, 94, 165, 8, 102, 238, 214, 183, 86, 138, 219, 52},
+			Encrypted: []byte{146, 217, 250, 254, 70, 201, 27, 221, 92, 145, 77, 213, 211, 197, 63, 189, 220, 188, 78, 8, 217, 108, 136, 89, 156, 23, 179, 54, 209, 54, 244, 170, 182, 150, 242, 52, 112, 191, 216, 46},
+			Expect:    []byte("goodbye mars"),
+		},
+	}
+
+	for i, test := range tests {
+		if len(test.AESKey) == 0 {
+			key, err := keygen.NewAESKey()
+			if err != nil {
+				t.Errorf("Test #%d: failed to generate new AES key: %s", i, err)
+				continue
+			}
+			test.AESKey = key
+		}
+
+		if len(test.Encrypted) == 0 {
+			enc, err := keygen.EncryptWithAESKey(test.Input, test.AESKey)
+			if err != nil {
+				t.Errorf("Test #%d: failed to encrypt input: %s", i, err)
+				continue
+			}
+			test.Encrypted = enc
+		}
+
+		// t.Errorf("Key: %+v\nEnc: %+v", test.AESKey, test.Encrypted)
+
+		dec, err := keygen.DecryptWithAESKey(test.Encrypted, test.AESKey)
+		if err != nil {
+			t.Errorf("Test #%d: failed to decrypt: %s", i, err)
+			continue
+		}
+
+		// compare the results
+		var ok = true
+		if len(dec) != len(test.Expect) {
+			ok = false
+		} else {
+			for j := range dec {
+				if test.Expect[j] != dec[j] {
+					ok = false
+				}
+			}
+		}
+		if !ok {
+			t.Errorf("Test #%d: got unexpected result from decrypt. Expected %s, got %s", i, test.Expect, dec)
+			continue
+		}
+	}
+}

pkg/encryption/keygen/keygen.go

@@ -1,11 +0,0 @@
-// Package keygen provides the AES key initializer function.
-package keygen
-
-import "crypto/rand"
-
-// NewAESKey returns a 32-byte (AES 256 bit) encryption key.
-func NewAESKey() ([]byte, error) {
-	var result = make([]byte, 32)
-	_, err := rand.Read(result)
-	return result, err
-}

pkg/encryption/keygen/rsa.go

@@ -0,0 +1,99 @@
+// Package keygen provides the AES key initializer function.
+package keygen
+
+import (
+	"crypto"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/pem"
+	"os"
+
+	"code.nonshy.com/nonshy/website/pkg/log"
+)
+
+// NewRSAKeys will generate an RSA 2048-bit key pair.
+func NewRSAKeys() (*rsa.PrivateKey, error) {
+	privateKey, err := rsa.GenerateKey(rand.Reader, 2048)
+	return privateKey, err
+}
+
+// SerializePublicKey converts an RSA public key into an x509 PEM encoded byte string.
+func SerializePublicKey(publicKey crypto.PublicKey) ([]byte, error) {
+	// Encode the public key to PEM format.
+	x509EncodedPub, err := x509.MarshalPKIXPublicKey(publicKey)
+	if err != nil {
+		return nil, err
+	}
+	pemEncodedPub := pem.EncodeToMemory(&pem.Block{
+		Type:  "RSA PUBLIC KEY",
+		Bytes: x509EncodedPub,
+	})
+	return pemEncodedPub, nil
+}
+
+// DeserializePublicKey loads the RSA public key from the PEM encoded byte array.
+func DeserializePublicKey(pemEncodedPub []byte) (*rsa.PublicKey, error) {
+	// Decode the public key.
+	log.Error("decode public key: %s", pemEncodedPub)
+	blockPub, _ := pem.Decode(pemEncodedPub)
+	x509EncodedPub := blockPub.Bytes
+	genericPublicKey, err := x509.ParsePKIXPublicKey(x509EncodedPub)
+	if err != nil {
+		return nil, err
+	}
+	publicKey := genericPublicKey.(*rsa.PublicKey)
+	return publicKey, nil
+}
+
+// WriteRSAKeys writes the public and private RSA keys to .pem files on disk.
+func WriteRSAKeys(key *rsa.PrivateKey, privateFile, publicFile string) error {
+	// Encode the private key to PEM format.
+	x509Encoded := x509.MarshalPKCS1PrivateKey(key)
+	pemEncoded := pem.EncodeToMemory(&pem.Block{
+		Type:  "RSA PRIVATE KEY",
+		Bytes: x509Encoded,
+	})
+
+	// Encode the public key to PEM format.
+	pemEncodedPub, err := SerializePublicKey(key.Public())
+	if err != nil {
+		return err
+	}
+
+	// Write the files.
+	if err := os.WriteFile(privateFile, pemEncoded, 0600); err != nil {
+		return err
+	}
+	if err := os.WriteFile(publicFile, pemEncodedPub, 0644); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// PrivateKeyFromFile loads the private key from disk.
+func PrivateKeyFromFile(privateFile string) (*rsa.PrivateKey, error) {
+	// Read the private key file.
+	pemEncoded, err := os.ReadFile(privateFile)
+	if err != nil {
+		return nil, err
+	}
+
+	// Decode the private key.
+	block, _ := pem.Decode(pemEncoded)
+	x509Encoded := block.Bytes
+	privateKey, _ := x509.ParsePKCS1PrivateKey(x509Encoded)
+	return privateKey, nil
+}
+
+// PublicKeyFromFile loads the public key from disk.
+func PublicKeyFromFile(publicFile string) (*rsa.PublicKey, error) {
+	pemEncodedPub, err := os.ReadFile(publicFile)
+	if err != nil {
+		return nil, err
+	}
+
+	// Decode the public key.
+	return DeserializePublicKey(pemEncodedPub)
+}

web/templates/admin/dashboard.html

@@ -9,6 +9,13 @@
         </div>
     </section>
 
+    <!-- Cold Storage warning -->
+    {{if .ColdStorageWarning}}
+    <div class="notification is-danger is-light mt-4">
+        <strong>Cold Storage Warning:</strong> {{.ColdStorageWarning}}.
+    </div>
+    {{end}}
+
     <div class="block p-4">
         <div class="columns">