Implement DARE 2.0

[aead]

This change adds a DARE 2.0 implementation for en/decrypting io.Reader and io.Writer. Further it adds a generic decrypted reader/writer to handle 1.0/2.0 compatibility.

• The default for encrypting io.Reader/io.Writer is DARE 2.0
• The default for decrypting io.Reader/io.Writer is DARE 1.0 and 2.0. (backward compatible)

This change also separates the DARE implementations from the io.Reader/io.Writer
implementations to make reasoning about the code easier. As part of this separation
this change adds new test vectors for DARE 1.0 and 2.0.

Fixes #16

[harshavardhana]

Will test this today @aead with the new encryption support in server. Is there anything specific that needs to be done or should this be just a drop in replacement?

[harshavardhana]

Few questions i have are this

• Should we still allow users to specify the version such that they can use Dare 1.0 ? if yes then why? - IMO we shouldn't allow them to create encrypted streams with 1.0 anymore.
• Can more comments be added in decrypter/reader implementation, helps in the review process.

[aead]

Is there anything specific that needs to be done or should this be just a drop in replacement?

Nothing to do - it's full backward compatible and can be used as drop-in replacement. sio will automatically adapt. Updating the vendor'd package at minio/minio should be all we have to do.

[aead]

Should we still allow users to specify the version such that they can use Dare 1.0 ? if yes then why? - IMO we shouldn't allow them to create encrypted streams with 1.0 anymore.

This would be not strictly backward compatible. First DARE 2.0 will be automatically selected except the user specifies: Config{MaxVersion: Version10}. So a user must explicitly request for 1.0 to encrypt a steam using DARE 1.0. However we can disallow 1.0 if we are willing to break existing code eventually.

Can more comments be added in decrypter/reader implementation, helps in the review process.

Yes, I will add some comments.

[donatello]

@aead Where is the spec for 2.0? It does not seem to be present in the DARE.md file in the 2.0 branch.

[aead]

@donatello Yes, the spec is not finalized yet (it's missing some performance numbers a.s.o)
Since we need 2.0 for SSE-C multipart I was trying get the implementation done. I'll amend it as soon as finished. I can send you the .tex file and the pdf.

[harshavardhana]

This would be not strictly backward compatible. First DARE 2.0 will be automatically selected except the user specifies: Config{MaxVersion: Version10}. So a user must explicitly request for 1.0 to encrypt a steam using DARE 1.0. However we can disallow 1.0 if we are willing to break existing code eventually.

No basically my point was on encryption we will disallow 1.0 but for decryption we allow.

[aead]

No basically my point was on encryption we will disallow 1.0 but for decryption we allow.

Yes, but imagine code using a config like: sio.Config{MaxVersion: Version10} for encryption right now would break. Of course I see that it would imply that the user would not use the more secure scheme. If we can pay the cost of breaking backward-compatible here(?) - I'm okay with disallowing 1.0 for encryption...

[harshavardhana]

Yes, but imagine code using a config like: sio.Config{MaxVersion: Version10} for encryption right now would break. Of course I see that it would imply that the user would not use the more secure scheme. If we can pay the cost of breaking backward-compatible here(?) - I'm okay with disallowing 1.0 for encryption...

We should disallow in my opinion and there is no need to override. Since decryption is backward compatible it shouldn't be a big problem.

[harshavardhana]

We should disallow in my opinion and there is no need to override. Since decryption is backward compatible it shouldn't be a big problem.

@abperiasamy suggested that we can be bit lenient here since sio is a separate package but we will default to 2.0 in Minio server.

[harshavardhana]

LGTM