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Home » Developing U++ » UppHub » Encrypted storage with streaming (OpenSSL, AES)
| Re: Encrypted storage with streaming (OpenSSL, AES) [message #25402 is a reply to message #25401] |
Mon, 22 February 2010 08:31   |
Mindtraveller
Messages: 917
Registered: August 2007
Location: Russia, Moscow rgn.
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| koldo wrote on Mon, 22 February 2010 09:54 |
1) Does it mean that AES cannot be used for saving user files with user defined password ?
However there are programs that include this possibility with AES. For example 7zip offers AES-256 encryption http://www.7-zip.org/7z.html.
2) Is there a standard way to convert a 8 chars user defined password into an useful 256 AES bits key ?
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1) Cryptography is no miracle, it's just math. If you use weak password, you get weak protection, and no algorithm saves you from it. This means if you want stable and strong protection, you must use stable and strong key. The one of few options here is to use key generated by OpenSSL itself.
You have to consider user password as worst type of key. Also, many passwords are too plain and dumb: 123, 111, 123456, etc. This is bad for cryptography.
Russian programmer Igor Pavlov who wrote 7zip, has chosen to use compromise solution. He takes user password, calculates SHA-256 function for it (AFAIK U++ has its realization too). Then he adds some calculations/changes to that 256-bit value and the final value is used as a key for AES encryption.
This represents fair protection, which is very much stronger than using user password as key, but at some rate weaker protection than with OpenSSL-generated key. In a number of uses it is rather good and satisfactory protection. Also it allows using protection without storing user password itself which is very good practice. But frankly speaking I haven't heard of SHA output as extremely cryptographically strong combination of bytes. This algorithm has another application field (generating unique digest "far" from original bytes).
2) AFAIK there is no "standard" way to convert user password to key. The best way is to use OpenSSL generated key. You may of course use any function like SHA-256 but you must be aware of the crytpographic strongness/weakness you give to user.
[Updated on: Mon, 22 February 2010 08:43] Report message to a moderator |
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| Re: Encrypted storage with streaming (OpenSSL, AES) [message #25403 is a reply to message #25402] |
Mon, 22 February 2010 08:50 |
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koldo
Messages: 3402
Registered: August 2008
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Senior Veteran |
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| Mindtraveller wrote on Mon, 22 February 2010 08:31 |
| koldo wrote on Mon, 22 February 2010 09:54 |
1) Does it mean that AES cannot be used for saving user files with user defined password ?
However there are programs that include this possibility with AES. For example 7zip offers AES-256 encryption http://www.7-zip.org/7z.html.
2) Is there a standard way to convert a 8 chars user defined password into an useful 256 AES bits key ?
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1) Cryptography is no miracle, it's just math. If you use weak password, you get weak protection, and no algorithm saves you from it. This means if you want stable and strong protection, you must use stable and strong key. The one of few options here is to use key generated by OpenSSL itself.
You have to consider user password as worst type of key. Also, many passwords are too plain and dumb: 123, 111, 123456, etc. This is bad for cryptography.
Russian programmer Igor Pavlov who wrote 7zip, has chosen to use compromise solution. He takes user password, calculates SHA-256 function for it (AFAIK U++ has its realization too). Then he adds some calculations/changes to that 256-bit value and the final value is used as a key for AES encryption.
This represents fair protection, which is very much stronger than using user password as key, but at some rate weaker protection than with OpenSSL-generated key. In a number of uses it is rather good and satisfactory protection. Also it allows using protection without storing user password itself which is very good practice. But frankly speaking I haven't heard of SHA output as extremely cryptographically strong combination of bytes. This algorithm has another application field (generating unique digest "far" from original bytes).
2) AFAIK there is no "standard" way to convert user password to key. The best way is to use OpenSSL generated key. You may of course use any function like SHA-256 but you must be aware of the crytpographic strongness/weakness you give to user.
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Excellent explanation 
I will follow your advice. Anyway, could you add a function to convert an username password into a "fair" protection ?. Thanks
I have checked your demo and now it works well. In a big program where I have applied it, it works well too .
You have done more changes than just a fix  . You have removed dependencies to packages Web and Web/SSL.
This afternoon I will upload it to Bazaar. In some hours I will propose a possible application of your useful functions.
Great job !
Best regards
Iñaki
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| Re: Encrypted storage with streaming (OpenSSL, AES) [message #25420 is a reply to message #25415] |
Mon, 22 February 2010 15:19 |
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Koldo,
Can you ad in BAZAAR?
Than you Koldo, and Mindtraveller!
Regards, ion Lupascu (tojocky).
| koldo wrote on Mon, 22 February 2010 13:46 |
Hello Mindtraveller
Your package is very useful.
If somebody requires to encrypt seriously a String or raw data from small size to Gb, this is a simple way to do it .
This is not an encryption algorithms catalog. This is just one of the best options with an easy interface.
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| Re: Encrypted storage with streaming (OpenSSL, AES) [message #25762 is a reply to message #25758] |
Wed, 10 March 2010 20:54 |
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kohait00
Messages: 939
Registered: July 2009
Location: Germany
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Experienced Contributor |
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hi koldo,
as far as i got the point of mindtraveler, AES and the other symetric algorithms are not to be thought of beeing based on a "password", a user defined and therefore week combination of signs (which would be scanned first in a brute force attack), but on a statistically well distributed *binary* key (128 bit should be made wise . it is hard for a human beeing to generate one. so the computer will take over and provide some random ones(AES key generator). this key should be thought of as a "password", what it of corse isn't. everything else would diminish the stability of the key.
maybe to get over it, think of it as kind a GUID which you generate once for your application (which in real world communication does not apply . dont think of AES as sort of alphanumerical password dependant encryption algorithm, it's indeed, just as mindtraveler mentioned: math. i had the luck to enjoy some lectures cryptology, and it confuses sometimes. but the first thing we learned there was to forget the idea of passwords / human readable strings as security base.
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| Re: Encrypted storage with streaming (OpenSSL, AES) [message #25763 is a reply to message #25762] |
Wed, 10 March 2010 21:33 |
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koldo
Messages: 3402
Registered: August 2008
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Senior Veteran |
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| kohait00 wrote on Wed, 10 March 2010 20:54 |
hi koldo,
as far as i got the point of mindtraveler, AES and the other symetric algorithms are not to be thought of beeing based on a "password", a user defined and therefore week combination of signs (which would be scanned first in a brute force attack), but on a statistically well distributed *binary* key (128 bit should be made wise . it is hard for a human beeing to generate one. so the computer will take over and provide some random ones(AES key generator). this key should be thought of as a "password", what it of corse isn't. everything else would diminish the stability of the key.
maybe to get over it, think of it as kind a GUID which you generate once for your application (which in real world communication does not apply . dont think of AES as sort of alphanumerical password dependant encryption algorithm, it's indeed, just as mindtraveler mentioned: math. i had the luck to enjoy some lectures cryptology, and it confuses sometimes. but the first thing we learned there was to forget the idea of passwords / human readable strings as security base.
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Yes yes, all of you are right
However think about for example a file encrypting software to be used by different people. How would you do it ?
Option 1: The software gives the user a 32 bytes random key
Option 2: The user enters a key
Option 1 seems much stronger. However file and hard disk encrypting software seems to choose option 2.
Best regards
Iñaki
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| Re: Encrypted storage with streaming (OpenSSL, AES) [message #25770 is a reply to message #25767] |
Thu, 11 March 2010 09:12 |
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koldo
Messages: 3402
Registered: August 2008
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Senior Veteran |
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Hello Kohait00
Thank you for the reference. I will use it.
Coming to the issue, look at this:
- If it is open source, I cannot put the key in the code
- If the program creates a key for the user, and he/she is not let to change it, a 32 bytes password seems too hard to use
- If we use a user defined key, we could include in AESStream:
---1. A SHA 256 possibility to convert user password in a 32 bytes key
---2. The means to avoid a brute force attack.
For example, if AES 256 with a weak user key can resist within and acceptable probability, for example, 1000000 random keys, AESStream could let the main program to enter, for example, 1000 keys per day and after that, AESStream would refuse any additional key.
Best regards
Iñaki
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| Re: Encrypted storage with streaming (OpenSSL, AES) [message #25772 is a reply to message #25770] |
Thu, 11 March 2010 10:29 |
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kohait00
Messages: 939
Registered: July 2009
Location: Germany
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Experienced Contributor |
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i dont know if i remember it correctly, but there are several technices combined to achieve encryption of data trggered by a user password.
1) the en/de cryption is done using a *fast* (symetrical) algorithm, like AES (they are blockorientated and relatively similar, only differ in their block functions (F functions, or Feistel Function)
2) the key used there, is the key we were speaking about, and is encrypted and stored with the data. as encryption can be used slow but really strong asymetrical (public / private key) algorithms like RSA.
3) the password thing comes into play with things like diffie hellman secure exchage of information with having it travel over the net.
but its quite a while now, and i may mix it up with things like vpn tunneling and handshaking and so on..
but in any way: encrypting decrypting to fit current standards is far from beeing trivial and involves a lot of steps, password is only a small part of it, maybe we should stick to common technologie here (means in openssl)
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