feat(api): add CryptoService for secret encryption (MS22-P1b)

apps/api/src/crypto/crypto.service.ts

@@ -0,0 +1,82 @@
+import { Injectable } from "@nestjs/common";
+import { ConfigService } from "@nestjs/config";
+import { createCipheriv, createDecipheriv, hkdfSync, randomBytes } from "crypto";
+
+const ALGORITHM = "aes-256-gcm";
+const ENCRYPTED_PREFIX = "enc:";
+const IV_LENGTH = 12;
+const AUTH_TAG_LENGTH = 16;
+const DERIVED_KEY_LENGTH = 32;
+const HKDF_SALT = "mosaic.crypto.v1";
+const HKDF_INFO = "mosaic-db-secret-encryption";
+
+@Injectable()
+export class CryptoService {
+  private readonly key: Buffer;
+
+  constructor(private readonly config: ConfigService) {
+    const secret = this.config.get<string>("MOSAIC_SECRET_KEY");
+
+    if (!secret) {
+      throw new Error("MOSAIC_SECRET_KEY environment variable is required");
+    }
+
+    if (secret.length < 32) {
+      throw new Error("MOSAIC_SECRET_KEY must be at least 32 characters");
+    }
+
+    this.key = Buffer.from(
+      hkdfSync(
+        "sha256",
+        Buffer.from(secret, "utf8"),
+        Buffer.from(HKDF_SALT, "utf8"),
+        Buffer.from(HKDF_INFO, "utf8"),
+        DERIVED_KEY_LENGTH
+      )
+    );
+  }
+
+  encrypt(plaintext: string): string {
+    const iv = randomBytes(IV_LENGTH);
+    const cipher = createCipheriv(ALGORITHM, this.key, iv);
+    const ciphertext = Buffer.concat([cipher.update(plaintext, "utf8"), cipher.final()]);
+    const authTag = cipher.getAuthTag();
+    const payload = Buffer.concat([iv, ciphertext, authTag]).toString("base64");
+
+    return `${ENCRYPTED_PREFIX}${payload}`;
+  }
+
+  decrypt(encrypted: string): string {
+    if (!this.isEncrypted(encrypted)) {
+      throw new Error("Value is not encrypted");
+    }
+
+    const payloadBase64 = encrypted.slice(ENCRYPTED_PREFIX.length);
+
+    try {
+      const payload = Buffer.from(payloadBase64, "base64");
+      if (payload.length < IV_LENGTH + AUTH_TAG_LENGTH) {
+        throw new Error("Encrypted payload is too short");
+      }
+
+      const iv = payload.subarray(0, IV_LENGTH);
+      const authTag = payload.subarray(payload.length - AUTH_TAG_LENGTH);
+      const ciphertext = payload.subarray(IV_LENGTH, payload.length - AUTH_TAG_LENGTH);
+
+      const decipher = createDecipheriv(ALGORITHM, this.key, iv);
+      decipher.setAuthTag(authTag);
+
+      return Buffer.concat([decipher.update(ciphertext), decipher.final()]).toString("utf8");
+    } catch {
+      throw new Error("Failed to decrypt value");
+    }
+  }
+
+  isEncrypted(value: string): boolean {
+    return value.startsWith(ENCRYPTED_PREFIX);
+  }
+
+  generateToken(): string {
+    return randomBytes(32).toString("hex");
+  }
+}