Some questions

[Stephen]

I’ve been having a look through the technical details on this website and I couldn’t find the answer to my question so hopefully somebody can answer it here.

I was reading this post by Svante:

“So, just to be clear, we do not store your password on the server.”

But here:

“We do have your password transiently on the server though, when we decrypt above-mentioned files, and it also travels over the internet encrypted with SSL.”

And here:

“In the future we might devise an authentication scheme for the server that does not require the actual transmission of the password, such as is normally done.”

I understand this comment to mean that you sign into the application, this transmits your password to the server, it’s validated (i.e. correct or incorrect) and then the server discards the password.

But I’m confused after reading this post:

“You are right that we do have an issue with the intuitive feeling that it’s bad to have the password sent to a server.”

Also:

“After that, all you’ll need is your new password to AxCrypt 2. The same one for files and for server based services.”

And:

“A file that was encrypted using a given password is always encrypted with that password, and you can always open the file with that password. It can also be opened with the account password, *unless* you do a password *reset* on the account.”

 

• Is it true to say that your encryption password is the same as the password you log into this website with?

• The website has a warning stating that “any encrypted files or information stored in the online password manager” will be lost if you forget your password.
  • What then does the password reset function do?
    • Does it regenerate a public/private key pair?
    • Is the old key pair destroyed?
    • What happens if you subsequently remember your password?
    • If you forgot your password [P1], reset it to something else [P2] and then remembered your old one would reverting it to [P1] allow you access to your data again?

• The other comment states an encrypted file can be opened “with that password” and “the account password”. If there’s only one password, what does this comment mean?

• What is the difference between changing and resetting a password?
  • “There is thus a definitive difference between *changing* and *resetting* AxCrypt ID online passwords. *resetting* can be done by a ‘hacker’ with access to your email. *changing* requires to really know the old password.” Source
    • If AxCrypt don’t store users’ files online then how could a hacker change the password to my files (assuming my system wasn’t hacked)?

• What’s the point in changing your password if your files are still accessible using the old password?
  • “Yes, that’s one of the nice things with AxCrypt 2. A changed password will work an all files previously encrypted with your AxCrypt ID (account, i.e. using your email address).” Source
    • Is there any way to change your password so that the old one will cease working on the files?
    • If you’re using a private key pair to do the encryption then surely changing its password would cause the old password to cease functioning?

• If I share an AxCrypt file with a non-Axcrypt user they’ll have to sign-up to view the file. Upon signing-up they’ll be given a free trial of premium. After their free trial has expired will they still be able to view any files I send them and modify and re-encrypt the file assuming they’re a free user?
  • “Premium is required to share with someone, but the sharee does not need Premium” Source

Sorry for the all the questions but I’ve looked around in the forums and I’ve been unable to find the answer and the information I have come across seems conflicting/contradictory.

[Stephen]

After submitting the post above I was unable to see it in the forums.

I pressed back and realised I hadn’t created a ‘Topic Title’; luckily all my text was still cached. There’s no warning/error validation from this website when you press ‘Submit’ that the post hasn’t been submitted correctly.

[Stephen]

One more question:

• Assume a premium user has shared a file with a free user:
  • Will the free user encrypt with AES-256 or AES-128 considering one user is premium and the other isn’t?

[SvanteSpectator]

Hello Stephen,

Well – I can’t say you didn’t do your homework ;-) I’ll try to respond, but to be honest, it’s a little hard to determine exactly what the questions are. But I’ll try. All answers assume that AxCrypt is used in online mode. (There are some variations to the theme in offline mode.) For followups, can you perhaps be careful to distinguish background info and assertions, from the actual questions? I try to answer, but it’s easy to miss something when the questions are not clearly separated and stated.

Q: Is the encryption password the same as the web sign in password?

A: Yes, when signed in to AxCrypt, all *encryption* is done using that password which is also the same as the web sign in. See below for details.

Q: What does password reset do?

A: It creates a new key pair, and encrypts the private key with the new password. The old key pair is kept around, should you ever change back to the original password.

Q: Can a hacker change the password to your files?

A: No. A hacker with control over your email can *reset* the password to the server (see above). This does not change anything or let the hacker open your encrypted files. Once you have regained control over your email, you can reset the password back to the original.

Q: Can a trial user open/encrypt/modify files key shared with them after the trial expires?

A: Yes. New encryption operations will use AES-128, but otherwise it all keeps on working.

Q: Can you change your password and also invalidate the old one for all old files?

A: No, not really. It’s complicated. See below for a technical explanation of how file encryption works.

—

How does file encryption with AxCrypt 2 and AxCrypt ID work?

An AxCrypt ID is a public key pair, using RSA-4096. The public key is used for encryption, and is non-secret. The private key is used for decryption, and is kept encrypted using your sign in / web password.

When a file is encrypted, the following operations take place:

1) A random 128 or 256-bit key is generated. We call this the file master key (or session key).

2) The file content is encrypted using this master key, and the encrypted data is stored in the .axx file.

3) The file master key is ‘wrapped’, i.e. iteratively encrypted using AES and a key derived from your sign in password. This wrapped file master key is also stored in the .axx file, as headers and trailers.

4) The file master key is also encrypted using your AxCrypt ID public key. This encrypted file master key is also stored in the .axx file, as headers and trailers.

5) (optional) The file master key is also encrypted using key sharing recipients’ AxCrypt ID public keys. These encrypted file master keys are also stored in the .axx file, as headers and trailers.

When you change your password, your private key is decrypted using the old password, and then encrypted again using your new password.

When you sign in, the password is verified by attempting to decrypt your private key.

When you decrypt a file, we first try to decrypt the file master key using your private key (decrypted since you’re signed in). If this works, we decrypt the file contents using the now decrypted file master key.

If that does not work, we try to use the sign in password to decrypt the iteratively wrapped encrypted file master key as described above. If this works, we decrypt the file contents using the now decrypted file master key.

If this does not work – we prompt you for a different password.

[Stephen]

Thank you for that comprehensive answer Svante :-)

What had originally confused me was how an old password could be used to decrypt a file if the key pairs were being regenerated. However I now understand that you retain the old key pair(s) so that if a user resets his password (and subsequently remembers his old one) that he can still decrypt previously encrypted data. Depending upon how many times a user forgets his password you may end up with a lot of key pairs on your servers!

I also wasn’t exactly clear on the difference between a password reset and a change but I now believe this to mean:

• A password reset regenerates the key pairs
• A password change re-wraps the existing key pairs

Assuming that I’ve understood your answers (i.e. my summary above is correct) then the only question I’d like clarification on is this:

“Yes. New encryption operations will use AES-128, but otherwise it all keeps on working.”

If as a premium user I share an AES-256 encrypted file with a free user will it still encrypt with AES-128 even though they’re sharing with a premium user?

Thanks again. ;-)

[SvanteSpectator]

Stephen,

First – you’re partially correct on how an old password can be used to decrypt a file after the key pair is regenerated or otherwise lost. The other thing is that when a file is encrypted, the file master key is also encrypted symmetrically with the password in effect at that time. So, you can always decrypt a file, even without the key pair, if you know the password in effect at the time of encryption. This is a measure to reduce the risk of data loss. The most common cause of data loss in Windows is loss of the key pair associated with the Encrypting File System, EFS. We don’t want AxCrypt to have the same problem.

Second – When a Premium user sends an AES-256 to a free user, that free user can open it (if (s)he has the password / keypair). If (s)he updates the file causing it to be re-encrypted, it’ll be encrypted with AES-128.

In summary: Premium: Decrypts all. Encrypts with AES-256. Free: Decrypts all. Encrypts with AES-128.

[Author]

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