mirror of
https://github.com/pgpainless/pgpainless.git
synced 2024-11-22 04:12:06 +01:00
Add more docs for Policy related configuration
This commit is contained in:
parent
507b36468b
commit
1452af71fd
GPG key ID:
62BEE9264BF17311
1 changed files with 162 additions and 0 deletions
|
|
@ -325,4 +325,166 @@ verificationStream.close(); // finish verification
|
|||
|
||||
MessageMetadata result = verificationStream.getMetadata(); // get metadata of signed message
|
||||
assertTrue(result.isVerifiedSignedBy(certificate)); // check if message was in fact signed
|
||||
```
|
||||
|
||||
### Legacy Compatibility
|
||||
Out of the box, PGPainless is configured to use secure defaults and perform checks for recommended
|
||||
security features. This means that for example messages generated using older OpenPGP
|
||||
implementations which do not follow those best practices might fail to decrypt/verify.
|
||||
|
||||
It is however possible to circumvent certain security checks to allow processing of such messages.
|
||||
|
||||
:::{note}
|
||||
It is not recommended to disable security checks, as that might enable certain attacks on the OpenPGP protocol.
|
||||
:::
|
||||
|
||||
#### Missing / broken MDC (modification detection code)
|
||||
RFC4880 has two different types of encrypted data packets. The *Symmetrically Encrypted Data* packet (SED) and the *Symmetrically Encrypted Integrity-Protected Data* packet.
|
||||
The latter has an added MDC packet which prevents modifications to the ciphertext.
|
||||
|
||||
While implementations are highly encouraged to only use the latter package type, some older implementations still generate
|
||||
encrypted data packets which are not integrity protected.
|
||||
|
||||
To allow PGPainless to decrypt such messages, you need to set a flag in the `ConsumerOptions` object:
|
||||
```java
|
||||
ConsumerOptions options = ConsumerOptions.get()
|
||||
.setIgnoreMDCErrors(true) // <-
|
||||
.setDecryptionKey(secretKey)
|
||||
...
|
||||
|
||||
DecryptionStream decryptionStream = PGPainless.decryptAndOrVerify()
|
||||
.onInputStream(ciphertextIn)
|
||||
.withOptions(options);
|
||||
...
|
||||
```
|
||||
|
||||
:::{note}
|
||||
It is highly advised to only set this flag if you know what you are doing.
|
||||
It might also be a good idea to try decrypting a message without the flag set first and only re-try
|
||||
decryption with the flag set in case of a `MessageNotIntegrityProtectedException` (don't forget to rewind the ciphertextInputStream).
|
||||
:::
|
||||
|
||||
#### Weak keys and broken algorithms
|
||||
Some users might cling on to older keys using weak algorithms / small key sizes.
|
||||
PGPainless refuses to encrypt to weak certificates and sign with weak keys.
|
||||
By default, PGPainless follows the recommendations for acceptable key sizes of [the German BSI in 2021](https://www.bsi.bund.de/SharedDocs/Downloads/EN/BSI/Publications/TechGuidelines/TG02102/BSI-TR-02102-1.pdf).
|
||||
It can however be configured to accept older key material / algorithms too.
|
||||
|
||||
Minimal key lengths can be configured by changing PGPainless' policy:
|
||||
```java
|
||||
Map<PublicKeyAlgorithm, Integer> algorithms = new HashMap<>();
|
||||
// put all acceptable algorithms and their minimal key length
|
||||
algorithms.put(PublicKeyAlgorithm.RSA_GENERAL, 1024);
|
||||
algorithms.put(PublicKeyAlgorithm.ECDSA, 100);
|
||||
...
|
||||
Policy.PublicKeyAlgorithmPolicy pkPolicy =
|
||||
new Policy.PublicKeyAlgorithmPolicy(algorithms);
|
||||
// set the custom algorithm policy
|
||||
PGPainless.getPolicy().setPublicKeyAlgorithmPolicy();
|
||||
```
|
||||
|
||||
Since OpenPGP uses a hybrid encryption scheme of asymmetric and symmetric encryption algorithms,
|
||||
it also comes with a policy for symmetric encryption algorithms.
|
||||
This list can be modified to allow for weaker algorithms like follows:
|
||||
```java
|
||||
// default fallback algorithm for message encryption
|
||||
SymmetricKeyAlgorithm fallbackAlgorithm = SymmetricKeyAlgorithm.AES_256;
|
||||
// acceptable algorithms
|
||||
List<SymmetricKeyAlgorithm> algorithms = new ArrayList<>();
|
||||
algorithms.add(SymmetricKeyAlgorithm.AES_256);
|
||||
algorithms.add(SymmetricKeyAlgorithm.AES_192);
|
||||
algorithms.add(SymmetricKeyAlgorithm.AES_128);
|
||||
algorithms.add(SymmetricKeyAlgorithm.TWOFISH);
|
||||
algorithms.add(SymmetricKeyAlgorithm.BLOWFISH);
|
||||
...
|
||||
Policy.SymmetricKeyAlgorithmPolicy skPolicy =
|
||||
new SymmtricKeyAlgorithmPolicy(fallbackAlgorithm, algorithms);
|
||||
// set the custom algorithm policy
|
||||
// algorithm policy applicable when decrypting messages created by legacy senders:
|
||||
PGPainless.getPolicy()
|
||||
.setSymmetricKeyDecryptionAlgorithmPolicy(skPolicy);
|
||||
// algorithm policy applicable when generating messages for legacy recipients:
|
||||
PGPainless.getPolicy()
|
||||
.setSymmetricKeyEncryptionAlgorithmPolicy(skPolicy);
|
||||
```
|
||||
|
||||
Hash algorithms are used in OpenPGP to create signatures.
|
||||
Since signature verification is an integral part of the OpenPGP protocol, PGPainless comes
|
||||
with multiple policies for acceptable hash algorithms, depending on the use-case.
|
||||
Revocation signatures are critical, so you might want to handle revocation signatures differently from normal signatures.
|
||||
|
||||
By default, PGPainless uses a smart hash algorithm policy for both use-cases, which takes into consideration
|
||||
not only the hash algorithm itself, but also the creation date of the signature.
|
||||
That way, signatures using SHA-1 are acceptable if they were created before February 2013, but are rejected if their
|
||||
creation date is after that point in time.
|
||||
|
||||
A custom hash algorithm policy can be set like this:
|
||||
```java
|
||||
HashAlgorithm fallbackAlgorithm = HashAlgorithm.SHA512;
|
||||
Map<HashAlgorithm, Date> algorithms = new HashMap<>();
|
||||
// Accept MD5 on signatures made before 1997-02-01
|
||||
algorithms.put(HashAlgorithm.MD5,
|
||||
DateUtil.parseUTCDate("1997-02-01 00:00:00 UTC"));
|
||||
// Accept SHA-1, regardless of signature creation time
|
||||
algorithms.put(HashAlgorithm.SHA1, null);
|
||||
...
|
||||
Policy.HashAlgorithmPolicy hPolicy =
|
||||
new Policy.HashAlgorithmPolicy(fallbackAlgorithm, algorithms);
|
||||
// set policy for revocation signatures
|
||||
PGPainless.getPolicy()
|
||||
.setRevocationSignatureHashAlgorithmPolicy(hPolicy);
|
||||
// set policy for normal signatures (certifications and document signatures)
|
||||
PGPainless.getPolicy()
|
||||
.setSignatureHashAlgorithmPolicy(hPolicy);
|
||||
```
|
||||
|
||||
Lastly, PGPainless comes with a policy on acceptable compression algorithms, which currently accepts any
|
||||
compression algorithm.
|
||||
A custom compression algorithm policy can be set in a similar way:
|
||||
```java
|
||||
CompressionAlgorithm fallback = CompressionAlgorithm.ZIP;
|
||||
List<CompressionAlgorithm> algorithms = new ArrayList<>();
|
||||
algorithms.add(CompressionAlgorith.ZIP);
|
||||
algorithms.add(CompressionAlgorithm.BZIP2);
|
||||
...
|
||||
Policy.CompressionAlgorithmPolicy cPolicy =
|
||||
new Policy.CompressionAlgorithmPolicy(fallback, algorithms);
|
||||
PGPainless.getPolicy()
|
||||
.setCompressionAlgorithmPolicy(cPolicy);
|
||||
```
|
||||
|
||||
To prevent a class of attacks described in the [paper](https://www.kopenpgp.com/#paper)
|
||||
"Victory by KO: Attacking OpenPGP Using Key Overwriting",
|
||||
PGPainless offers the option to validate private key material each time before using it,
|
||||
to make sure that an attacker didn't tamper with the corresponding public key parameters.
|
||||
|
||||
These checks are disabled by default, but they can be enabled as follows:
|
||||
```java
|
||||
PGPainless.getPolicy()
|
||||
.setEnableKeyParameterValidation(true);
|
||||
```
|
||||
|
||||
:::{note}
|
||||
Validation checks against KOpenPGP attacks are disabled by default, since they are very costly
|
||||
and only make sense in certain scenarios.
|
||||
Please read and understand the paper to decide, if enabling the checks makes sense for your use-case.
|
||||
:::
|
||||
|
||||
|
||||
### Known Notations
|
||||
In OpenPGP, signatures can contain [notation subpackets](https://www.rfc-editor.org/rfc/rfc4880#section-5.2.3.16).
|
||||
A notation can give meaning to a signature, or add additional contextual information.
|
||||
Signature subpackets can be marked as critical, meaning an implementation that does not know about
|
||||
a certain subpacket MUST reject the signature.
|
||||
The same is true for critical notations.
|
||||
|
||||
For that reason, PGPainless comes with a `NotationRegistry` class which can be used to register known notations,
|
||||
such that a signature containing a critical notation of a certain value is not rejected.
|
||||
To register a known notation, you can do the following:
|
||||
|
||||
```java
|
||||
NotationRegistry registry = PGPainless.getPolicy()
|
||||
.getNotationRegistry();
|
||||
|
||||
registry.addKnownNotation("sample@example.com");
|
||||
```
|
||||
Loading…
Reference in a new issue