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pgpainless/docs/source/pgpainless-core/passphrase.md

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# Passwords
In Java based applications, passing passwords as `String` objects has the
[disadvantage](https://stackoverflow.com/a/8881376/11150851) that you have to rely on garbage collection to clean up
once they are no longer used.
For that reason, `char[]` is the preferred method for dealing with passwords.
Once a password is no longer used, the character array can simply be overwritten to remove the sensitive data from
memory.
## Passphrase
PGPainless uses a wrapper class `Passphrase`, which takes care for the wiping of unused passwords:
```java
Passphrase passphrase = new Passphrase(new char[] {'h', 'e', 'l', 'l', 'o'});
assertTrue(passphrase.isValid());
assertArrayEquals(new char[] {'h', 'e', 'l', 'l', 'o'}, passphrase.getChars()):
// Once we are done, we can clean the data
passphrase.clear();
assertFalse(passphrase.isValid());
assertNull(passphrase.getChars());
```
Furthermore, `Passphrase` can also wrap empty passphrases, which increases null-safety of the API:
```java
Passphrase empty = Passphrase.emptyPassphrase();
assertTrue(empty.isValid());
assertTrue(empty.isEmpty());
assertNull(empty.getChars());
empty.clear();
assertFalse(empty.isValid());
```
## SecretKeyRingProtector
There are certain operations that require you to provide the passphrase for a key.
Examples are decryption of messages, or creating signatures / certifications.
The primary way of telling PGPainless, which password to use for a certain key is the `SecretKeyRingProtector`
interface.
There are multiple implementations of this interface, which may or may not suite your needs:
```java
// If your key is not password protected, this implementation is for you:
SecretKeyRingProtector unprotected = SecretKeyRingProtector
.unprotectedKeys();
// If you use a single passphrase for all (sub-) keys, take this:
SecretKeyRingProtector singlePassphrase = SecretKeyRingProtector
.unlockAnyKeyWith(passphrase);
// If you want to be flexible, use this:
CachingSecretKeyRingProtector flexible = SecretKeyRingProtector
.defaultSecretKeyRingProtector(passphraseCallback);
```