Cryptography on Margrop Blog https://blog.margrop.net/en/tag/cryptography/ Recent content in Cryptography on Margrop Blog Hugo -- gohugo.io en-US Wed, 29 Jul 2026 20:30:00 +0800 Is Giving One App All Your Passwords Insane? The Math Behind a Master Password and an Encrypted Vault https://blog.margrop.net/en/post/password-manager-master-password-encrypted-vault-math/ Wed, 29 Jul 2026 20:30:00 +0800 https://blog.margrop.net/en/post/password-manager-master-password-encrypted-vault-math/ The short answer A well-designed password manager does not merely remember a readable spreadsheet of your passwords. It stores an encrypted vault. Your master password is not normally used as the raw encryption key for every item. Instead, your device sends it through a deliberately expensive key derivation function, obtains derived key material, unlocks a randomly generated vault key, and decrypts your records locally. The server mainly stores and synchronizes ciphertext. The Password Was Right—So Why Did Synology Reject It? Rebuilding DSM’s RSA + AES WebAPI Login https://blog.margrop.net/en/post/synology-webapi-login-encryption-deep-dive/ Sat, 11 Jul 2026 08:30:00 +0800 https://blog.margrop.net/en/post/synology-webapi-login-encryption-deep-dive/ <blockquote> <p><strong>The short version</strong></p> <p>Some Synology WebAPI clients do more than post <code>account</code> and <code>passwd</code> to <code>auth.cgi</code>. The implementation preserved in OpenStack Cinder first calls <code>SYNO.API.Encryption.getinfo</code>, receives an RSA public modulus, server time, and two dynamic field names, then generates a one-use passphrase. RSA PKCS#1 v1.5 encrypts that passphrase; an OpenSSL-compatible AES-256-CBC envelope encrypts the URL-encoded login parameters; both Base64 values are finally placed inside the server-provided <code>cipherkey</code> field.</p> <p>This is an authorized WebAPI compatibility technique—not a password bypass. A SID for <code>session=DSM</code> is also not automatically the same thing as a complete browser UI login state. Parameter encryption does not replace HTTPS, because TLS still authenticates the server and protects integrity against an active intermediary.</p> </blockquote> <p><img alt="Original cover: an RSA outer envelope and AES inner envelope protect a NAS login" src="https://blog.margrop.net/post-images/synology-webapi-login-encryption-deep-dive/00-cover-original.png"></p>