[racket] PLaneTs crypto lib usage question?...

ok, I figured out the raised exception part... turns out the OpenSSL  
interface is a little bit too rigurous with respect to lib failure  
returns; they are all translated  to raised errors. Can easily be  
eliminated by modifying check_error() in error.ss. But about the other  
question... very likely I don't understand enough about the meaning of  
init vectors, but shouldn' a strong encryption algorithm completly  
garble the cipher if only one part of the input changes to prevent  
attacks?...

Quoting Rüdiger Asche <rac at ruediger-asche.de>:

> I'm doodling around with vyzo's crypto lib from PLaneT, doing some very
> rudimentary crypting and encrypting. I'm undoubtedly doing something
> wrong, I just don't know what...
>
> Here's my code (running from a directory that contains the crypto files):
>
> (require srfi/78
>          "main.ss"
>          (only-in "util.ss" hex))
>
> (require file/sha1)
>
> (define devicekey (list->bytes '(#x12 #x34 #x56 #x78 #x87 #x65 #x43
> #x26 #x12 #x34 #x56 #x78 #x87 #x65 #x43 #x26)))  ; must be length 16!!!
>
> (define nonce (list->bytes '(#x12 #x34 #x56 #x78 #x87 #x65 #x43 #x26
> #x12 #x34 #x56 #x78 #x87 #x65 #x43 #x27)))  ; must be length 16!!!
>
> (define devicekey1 (list->bytes '(#x12 #x34 #x56 #x88 #x87 #x65 #x43
> #x26 #x12 #x34 #x56 #x78 #x87 #x65 #x43 #x26)))  ; must be length 16!!!
>
> (define nonce1 (list->bytes '(#x12 #x34 #x56 #x78 #x87 #x66 #x43 #x26
> #x12 #x34 #x56 #x78 #x87 #x65 #x43 #x27)))  ; must be length 16!!!
>
> (define dummy (encrypt cipher:aes-128 devicekey nonce #"1234567887654321"))
>
> (bytes->hex-string dummy)
>
> (decrypt cipher:aes-128 devicekey nonce dummy)
>
> (decrypt cipher:aes-128 devicekey1 nonce dummy)
>
> (decrypt cipher:aes-128 devicekey nonce1 dummy)
>
> In effect, I hardcode two distinct AES keys, 2 initialization vectors
> (wich I call nonce) and one piece of plain text to encrypt and decrypt.
>
> Here are the results of the last three lines when executed in Racket:
>
> (decrypt cipher:aes-128 devicekey nonce dummy)
> #"1234567887654321"                            <== 1
>>
> (decrypt cipher:aes-128 devicekey1 nonce dummy)
> EVP_CipherFinal_ex: libcrypto error: bad decrypt [digital envelope
> routines:EVP_
> DecryptFinal_ex:101077092]                     <== 2
>>
> (decrypt cipher:aes-128 devicekey nonce1 dummy)
> #"1234557887654321"                            <== 3
>
> So the first decryption (with the correct key and iv) yields the
> expected result. Everything fine here.
>
> When I decrypt with the correct iv but a wrong key, the OpenSSL Crypto
> Lib raises an error. I think that is wrong; it should simply return
> garbled output?
>
> And when I decrypt with the correct key but an invalid init vector, I
> would expect the decryption result to be radically different from the
> original; instead, there is only one byte varying as if the iv only
> does some weak manipulation on the input before doing the encryption?
> Is that the way AES-128 works?
>
> AES-192 is pretty much exactly the same:
>
> Welcome to Racket v5.2.1.
>> (require srfi/78
>          "main.ss"
>          (only-in "util.ss" hex))
>>
> (require file/sha1)
>>
> (define devicekey (list->bytes '(#x12 #x34 #x56 #x78 #x87 #x65 #x43
> #x26 #x12 #x
> 34 #x56 #x78 #x87 #x65 #x43 #x26 #x12 #x34 #x56 #x78 #x87 #x65 #x43
> #x26)))  ; m
> ust be length 24!!!
>>
> (define nonce (list->bytes '(#x12 #x34 #x56 #x78 #x87 #x65 #x43 #x26
> #x12 #x34 #
> x56 #x78 #x87 #x65 #x43 #x27 #x12 #x34 #x56 #x78 #x87 #x65 #x43 #x26)))
>  ; must
> be length 24!!!
>>
> (define devicekey1 (list->bytes '(#x12 #x34 #x56 #x88 #x87 #x65 #x43
> #x26 #x12 #
> x34 #x56 #x78 #x87 #x65 #x43 #x26 #x12 #x34 #x56 #x78 #x87 #x65 #x43
> #x26)))  ;
> must be length 24!!!
>>
> (define nonce1 (list->bytes '(#x12 #x34 #x56 #x78 #x87 #x66 #x43 #x26
> #x12 #x34
> #x56 #x78 #x87 #x65 #x43 #x27 #x12 #x34 #x56 #x78 #x87 #x65 #x43
> #x26)))  ; must
>  be length 24!!!
>>
> (define dummy (encrypt cipher:aes-192 devicekey nonce
> #"123456788765432112345678
> "))
>>
> (bytes->hex-string dummy)
> "a5de853635ea2f7a61d709a7e2c877db1c6b15929d9559ff51e1fd470c6bf4a8"
>>
> (decrypt cipher:aes-192 devicekey nonce dummy)
> #"123456788765432112345678"
>>
> (decrypt cipher:aes-192 devicekey1 nonce dummy)
> EVP_CipherFinal_ex: libcrypto error: bad decrypt [digital envelope
> routines:EVP_
> DecryptFinal_ex:101077092]
>>
> (decrypt cipher:aes-192 devicekey nonce1 dummy)
> #"123455788765432112345678"
>>
>
> Any ideas what is going on here?
>
> Thanks!
>
>
>
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