初始提交：DSH 多租户平台（dshs）

src/crypto.ts

@@ -0,0 +1,35 @@
+/**
+ * Symmetric encryption for per-user secrets at rest. AES-256-GCM with a
+ * key derived from the deployment secret, so a DB leak does not yield usable
+ * API keys (references-not-secrets).
+ * @module dshs/crypto
+ */
+
+import { createCipheriv, createDecipheriv, createHash, randomBytes } from 'node:crypto'
+
+const ALGO = 'aes-256-gcm'
+const IV_LEN = 12
+
+/** Derive a 32-byte AES key from the deployment secret (sha-256). */
+export function deriveKey(secret: string): Buffer {
+  return createHash('sha256').update(secret).digest()
+}
+
+/** Encrypt a plaintext secret into a base64 payload `iv.tag.data`. */
+export function encrypt(plain: string, key: Buffer): string {
+  const iv = randomBytes(IV_LEN)
+  const cipher = createCipheriv(ALGO, key, iv)
+  const enc = Buffer.concat([cipher.update(plain, 'utf8'), cipher.final()])
+  const tag = cipher.getAuthTag()
+  return [iv.toString('base64'), tag.toString('base64'), enc.toString('base64')].join('.')
+}
+
+/** Decrypt a payload produced by {@link encrypt}. */
+export function decrypt(payload: string, key: Buffer): string {
+  const parts = payload.split('.')
+  if (parts.length !== 3) throw new Error('malformed encrypted payload')
+  const [ivB, tagB, dataB] = parts as [string, string, string]
+  const decipher = createDecipheriv(ALGO, key, Buffer.from(ivB, 'base64'))
+  decipher.setAuthTag(Buffer.from(tagB, 'base64'))
+  return Buffer.concat([decipher.update(Buffer.from(dataB, 'base64')), decipher.final()]).toString('utf8')
+}