How to handle encrypted string?

Question

I am trying to make a simple application, which is able to encrypt and decrypt some simple data. CryptEncrypt is working fine. The string to encrypt is: This is a sample string.. The encrypted data for this string is: ¼╩b╒áó√ $~ë▀i▐└╕ ]Φwµσ╨|V╜▐µáïÅ╚ So far so good.

After i have the encrypted text, i copy it to another string. This string will be used at the decryption. For some reason only the half of the string wil be copied in the new buffer,a nd therefore it can't be decrypted. No matter how i try. I'm assumeing that in the encrypted string there are some special characters, and therefore it won't copied as expected. For example if i use sprintf(teststring,"%s",Encryptedstring); it will also copy only half of the string.

Is there a way to make CryptEncrypt encrypt the data in a hex form by default?
How should i copy my string correctly?

I suspect perhaps encryption is working in 8-bit bytes, and putting a 0 byte in the middle of the ciphertext. That will render it useless to C functions like strcpy(). You'll have to manage buffers yourself. — Lee Daniel Crocker
– Lee Daniel Crocker, Commented Nov 7, 2014 at 19:33
Encryption and decryption deal with data buffers, not strings (though string have associated data buffers). So you should use data copy functions (eg. memcpy) rather than string functions (such as strcpy and sprintf) — SleuthEye
– SleuthEye, Commented Nov 7, 2014 at 19:38

Deduplicator · Accepted Answer · 2014-11-07 20:55:13Z

2

You are making a basic mistake:

You are handing a c-string (I cannot say whether with or without the terminator) to CryptEncrypt and somehow expect magically to get a valid c-string of the same length back.

Things just don't work that way, the output of any good encryption-function looks like a pseudo-random binary blob, maybe with embedded 0-bytes, maybe not, and unlikely to have a terminating 0-byte.

Case in point, the output you gave is considerably longer than the input (The last part is probably garbage picked up due to missing 0-terminator).

The solution: Properly handle arbitrary binary data as arbitrary binary data (memcpy for copying).
If you want, you can encode it into some textual representation to get a string, but that's an extra step needing more space and certainly not the task of CryptEncrypt.

edited Nov 7, 2014 at 20:55

answered Nov 7, 2014 at 19:35

Deduplicator

46k7 gold badges73 silver badges125 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

awatan · Accepted Answer · 2014-11-07 19:39:58Z

2

My advice is that when you talk about encryption, do not talk in terms of strings. Your string is just a raw data block to an encryption function so deal with it accordingly. The problem with dealing the data as string is that string tends to terminate if a null character is found and there is every possibility that you will get null byte in encrypted block.

This is why string functions dont work with encrypted data. If you want to copy data from buffer to another buffer, use memcpy instead of sprintf or strcpy.

answered Nov 7, 2014 at 19:39

awatan

1,2101 gold badge16 silver badges34 bronze badges

Comments

Moumou · Accepted Answer · 2014-11-07 19:33:24Z

0

I guess that sprintf will stop the copy if it encounters a '\0' charcater. You should use memcpy

answered Nov 7, 2014 at 19:33

Moumou

1,5323 gold badges19 silver badges42 bronze badges

Collectives™ on Stack Overflow

How to handle encrypted string?

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related