encrypt in1st app, decrypt in 2nd app

[Arrie]

Hi Agraham,

The answers you gave were correct. Especially test4 (my name is Arjan). But when i create a new nickname in the first application, then there will be an error "CryptDecrypt failed at adress 0x8009005"

It appears when the original stringlength<6 everything works fine, but when it is 6 or more the abovementioned errormessage is shown.

Arrie

[agraham]

Originally Posted by Arrie

It appears when the original stringlength<6 everything works fine, but when it is 6 or more the abovementioned errormessage is shown.

That must be something in your code. Are you truncating the encrypted string somehow? If you download the Crypto example from here Basic4ppc - Windows Mobile programming and Pocket PC Development (use only the source file together with the latest libraries from the Basic4ppc Desktop\Libraries folder) and replace the key with your key it not only produces the samre results as your tests but aalso deals OK with strings longer than 6.

[Arrie]

Hi Agraham,

I'm not aware that the data is truncated. can you decrypt this string "a498a0f2283376354b96f58f3b5473f4", when the result is what i expect, the data is ok. The original line (before encryption ) is 9 digits.

Thanks,

Arrie

[agraham]

No, that fails with a bad data error. What was the original data?

[agraham]

The problem is with DecToHex, it doesn't always return two characters so the data is being truncated. You need something like this.

For i = 0 To ArrayLen(secret())-1
  If secret(i)< 16 Then s = s & "0"
  s = s & bit.DecToHex(secret(i))
Next

EDIT:- Typo in the code above corrected, was 15 now 16

[Arrie]

agraham @ 9:34 Original was Basic4PPC

[Arrie]

Oke Agraham,

So if i understood it correct, in the encryption of the data (in the 1st application) the truncade took place, and in the decryption of the data (in the 2nd application, we must use a prefix zero if the secret datapacket is smaller then 16(dec) or F(hex), is this correct ? And if so is this than a bug or just stupid programming from me

Greetings Arrie

[agraham]

Originally Posted by Arrie

we must use a prefix zero if the secret datapacket is smaller then 16(dec) or F(hex), is this correct ?

Actually smaller than 16(dec) = 10(hex). As the conversion from hex back to bytes assumes each byte is represented by a 2 character hex number then the original byte to hex must make sure that each bytes maps to a 2 character hex number. The library only produces a single hex character for values less than 16 so the "0" needs to be added to make it 2 characters.

And if so is this than a bug or just stupid programming from me

Neither, just a "feature" of the library you didn't know about.

[Arrie]

Oke, still working on this problem. Now if the original stringlength is unequal ie 15 etc. then the i in the For .... next statement will only go to 7. Is there a function to decide if the stringlength is unequal or equal. I don't know if i stated it correct, but i mean can the stringlength be divided by 2.

Arrie

[agraham]

Originally Posted by Arrie

Oke, still working on this problem.

You seem to be looking at the problem from the wrong end. The solution is in my post #15 above which you put in the encryption app to make sure the string length is an even number of characters.