code review 7854045: crypto/cipher: Added BlockReader and BlockWriter

crypto/cipher: Added BlockReader and BlockWriter

Wrapper for BlockMode ciphers that implement io.Reader and io.Writer
interfaces. PKCS7 padding was added, other padding methods should be
simple to implement in future commits.
Fixes issue 4968.

[fasmat, 2013-03-24 20:37:04]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go

[rsc, 2013-03-25 00:23:48]

Sorry, but we're not adding new API again until after Go 1.1 is released.
Please ping this thread then.

golang.org/s/go11freeze

[luke1, 2013-04-15 20:51:11]

On 2013/03/24 20:37:04, fasmat wrote:
> Hello mailto:golang-dev@googlegroups.com,
> 
> I'd like you to review this change to
> https://code.google.com/p/go

I do agree that padding needs to be added to the standard crypto library -
whether ever that ends up being in the future.

I don't think this should be in a reader/writer form though. Block ciphers are
typically used to encrypt complete messages - they aren't stream ciphers. I
would prefer a simple wrapper to crypto.BlockMode that implements the same
interface. Each padding scheme should also be a different package - something
like "crypto/cipher/pkcs7".

Something like this would be nice:

func NewPKCS7Encrypter(b crypto.BlockMode) BlockMode
func NewPKCS7Decrypter(b crypto.BlockMode) BlockMode
func AddPadding(data []byte, blockSize int) []byte
func RemovePadding(data []byte, blockSize int) []byte

[agl1, 2013-04-15 21:31:35]

Just while I see this go by: this is open to Vaudenay's attack. I can do a real
review if it gets reanimated after Go 1.1.

[fasmat, 2013-04-16 10:52:16]

On 2013/04/15 21:31:35, agl1 wrote:
> Just while I see this go by: this is open to Vaudenay's attack. I can do a
real
> review if it gets reanimated after Go 1.1.

I will look into this in the next days.

[fasmat, 2013-04-16 11:02:27]

On 2013/04/15 20:51:11, luke1 wrote:
> I do agree that padding needs to be added to the standard crypto library -
> whether ever that ends up being in the future.
> 
> I don't think this should be in a reader/writer form though. Block ciphers are
> typically used to encrypt complete messages - they aren't stream ciphers. I
> would prefer a simple wrapper to crypto.BlockMode that implements the same
> interface. Each padding scheme should also be a different package - something
> like "crypto/cipher/pkcs7".
> 
> Something like this would be nice:
> 
> func NewPKCS7Encrypter(b crypto.BlockMode) BlockMode
> func NewPKCS7Decrypter(b crypto.BlockMode) BlockMode
> func AddPadding(data []byte, blockSize int) []byte
> func RemovePadding(data []byte, blockSize int) []byte

I can improve the structure of the code by separating paddings into single
packages.

Concerning the reader/writer interfaces for block based ciphers: I'd like to
have something similar to CipherInputStream and CipherOutputStream of
javax.crypto as this makes code to read a block cipher encrypted file as easy as
reading stream cipher encrypted files.

Consider this scenario:
http://stackoverflow.com/questions/13108567/replicate-java-decryption-code-in...

I worked around it by using a byte buffer which works for smaller files but
could cause some issues with larger files on systems with limited memory.

[fasmat, 2013-05-09 19:05:37]

*** Abandoned ***

[rsc, 2013-12-18 20:14:07]

R=close