KeePass database files are encrypted. KeePass encrypts the whole database, i.e. not only your passwords, but also your user names, URLs, notes, etc.
The following encryption algorithms are supported:
These well-known and thoroughly analyzed algorithms are considered to be very secure. AES (Rijndael) became effective as a U.S. federal government standard and is approved by the National Security Agency (NSA) for top secret information. Twofish was one of the other four AES finalists. ChaCha20 is the successor of the Salsa20 algorithm (which is included in the eSTREAM portfolio).
The block ciphers are used in the Cipher Block Chaining (CBC) block cipher mode. In CBC mode, plaintext patterns are concealed.
KeePass 1.x OnlyThe authenticity and integrity of the data is ensured using a SHA-256 hash of the plaintext.
KeePass 2.x OnlyThe authenticity and integrity of the data is ensured using a HMAC-SHA-256 hash of the ciphertext (Encrypt-then-MAC scheme).
Key Hashing and Key Derivation
SHA-256 is used for compressing the components of the composite master key (consisting of a password, a key file, a Windows user account key and/or a key provided by a plugin) to a 256-bit key K.
SHA-256 is a cryptographic hash function that is considered to be very secure. It has been standardized in NIST FIPS 180-4. The attack against SHA-1 discovered in 2005 does not affect the security of SHA-256.
In order to generate the key for the encryption algorithm, K is transformed using a key derivation function (with a random salt). This prevents precomputation of keys and makes dictionary and guessing attacks harder. For details, see the section 'Protection against Dictionary Attacks'.
Protection against Dictionary Attacks
KeePass features a protection against dictionary and guessing attacks.
Such attacks cannot be prevented, but they can be made harder. For this, the key K derived from the user's composite master key (see above) is transformed using a key derivation function with a random salt. This prevents a precomputation of keys and adds a work factor that the user can make as large as desired to increase the computational effort of a dictionary or guessing attack.
The following key derivation functions are supported (they can be chosen and configured in the database settings dialog):
By clicking the '1 Second Delay' button in the database settings dialog, KeePass computes the number of iterations that results in a 1 second delay when loading/saving a database. Furthermore, KeePass 2.x has a button 'Test' that performs a key derivation with the specified parameters (which can be cancelled) and reports the required time.
The key derivation may require more or less time on other devices. If you are using KeePass or a port of it on other devices, make sure that all devices are fast enough (and have sufficient memory) to load the database with your parameters within an acceptable time.
KeePassX. In contrast to KeePass, the Linux port KeePassX only partially supports protection against dictionary and guessing attacks.
Random Number Generation
KeePass first creates an entropy pool using various entropy sources (including random numbers generated by the system cryptographic provider, current date/time and uptime, cursor position, operating system version, processor count, environment variables, process and memory statistics, current culture, a new random GUID, etc.).
The random bits for the high-level generation methods are generated using a cryptographically secure pseudo-random number generator (based on SHA-256/SHA-512 and ChaCha20) that is initialized using the entropy pool.
Process Memory Protection
While KeePass is running, sensitive data (like the hash of the master key and entry passwords) is stored encryptedly in process memory. This means that even if you would dump the KeePass process memory to disk, you could not find any sensitive data.
Furthermore, KeePass erases all security-critical memory when it is not needed anymore, i.e. it overwrites these memory areas before releasing them.
KeePass uses the Windows DPAPI for in-memory encrypting sensitive data (via CryptProtectMemory / ProtectedMemory). With DPAPI, the key for in-memory encryption is stored in a secure, non-swappable memory area managed by Windows. DPAPI is available on Windows 2000 and higher. KeePass 2.x always uses DPAPI when it is available; in KeePass 1.x, this can be disabled (in the advanced options; by default using DPAPI is enabled; if it is disabled, KeePass uses the ARC4 encryption algorithm with a random key; note that this is less secure than DPAPI, mainly not because ARC4 cryptographically is not that strong, but because the key for in-memory encryption is also stored in swappable process memory; similarly, KeePass 2.x falls back to encrypting the process memory using ChaCha20, if DPAPI is unavailable). On Unix-like systems, KeePass 2.x uses ChaCha20, because Mono does not provide any effective memory protection method.
For some operations, KeePass must make sensitive data available unencryptedly in process memory. For example, in order to show a password in the standard list view control provided by Windows, KeePass must supply the cell content (the password) as unencrypted string (unless hiding using asterisks is enabled). Operations that result in unencrypted data in process memory include, but are not limited to: displaying data (not asterisks) in standard controls, searching data, replacing placeholders (during auto-type, drag&drop, copying to clipboard, ...), and computing password quality estimations.
Enter Master Key on Secure Desktop (Protection against Keyloggers)
KeePass 2.x has an option (in 'Tools' -> 'Options' -> tab 'Security') to show the master key dialog on a different/secure desktop (supported on Windows 2000 and higher), similar to Windows' User Account Control (UAC). Almost no keylogger works on a secure desktop.
The option is turned off by default for compatibility reasons.
More information can be found on the Secure Desktop help page.
KeePass 2.x OnlyNote that auto-type can be secured against keyloggers, too, by using Two-Channel Auto-Type Obfuscation.
Note: KeePass was one of the first password managers that allow entering the master key on a different/secure desktop!
Locking the Workspace
When locking the workspace, KeePass closes the database file and only remembers its path.
This provides maximum security: unlocking the workspace is as hard as opening the database file the normal way. Also, it prevents data loss (the computer can crash while KeePass is locked, without doing any damage to the database).
KeePass 2.x has an internal viewer/editor for attachments. For details how to use it for working with texts, see 'How to store and work with large amounts of (formatted) text?'.
The internal viewer/editor works with the data in main memory. It does not extract/store the data onto disk.
When trying to open an attachment that the internal viewer/editor cannot handle (e.g. a PDF file), KeePass extracts the attachment to a (EFS-encrypted) temporary file and opens it using the default application associated with this file type. After finishing viewing/editing, the user can choose between importing or discarding any changes made to the temporary file. In any case, KeePass afterwards securely deletes the temporary file (including overwriting it).
Each time you start KeePass, the program performs a quick self-test to see whether the encryption and hash algorithms work correctly and pass their test vectors. If one of the algorithms does not pass its test vectors, KeePass shows a security exception dialog.
This section gives answers to questions like the following:
The answer to all these questions is: no. Adding any of these features would not increase security.
All security features in KeePass protect against generic threats like keyloggers, clipboard monitors, password control monitors, etc. (and against non-runtime attacks on the database, memory dump analyzers, ...). However in all the questions above we are assuming that there is a spyware program running on the system that is specialized on attacking KeePass.
In this situation, the best security features will fail.
This is law #1 of the
Ten Immutable Laws of Security
(Microsoft TechNet article; also see the
Microsoft TechNet article
Revisiting the 10 Immutable Laws of Security, Part 1):
For example, consider the following very simple spyware specialized for KeePass: an application that waits for KeePass to be started, then hides the started application and imitates KeePass itself. All interactions (like entering a password for decrypting the configuration, etc.) can be simulated. The only way to discover this spyware is to use a program that the spyware does not know about or cannot manipulate (secure desktop); in any case it cannot be KeePass.
For protecting your PC, we recommend using an anti-virus software. Use a proper firewall, only run software from trusted sources, do not open unknown e-mail attachments, etc.
For a list of security issues, their status and clarifications, please see the page Security Issues.