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The encryption uses a public/private keys to encrypt the files using the public key, while keeping the private key stored on the remote servers. The clients PC

The encryption uses a public/private keys to encrypt the files using the public key, while keeping the private key stored on the remote servers. The clients PC never has access to the decryption key. https://en.wikipedia.org/wiki/Public-key_cryptography https://en.wikipedia.org/wiki/Public-key_cryptography

Cyph0n 10y ago
Using PK crypto would be horrendously slow, especially if there are a large number of files. Besides, the article notes that this ransomware uses AES-256. Perhaps the AES key is encrypted with RSA after encryption is complete and kept on the infected machine.
- user5994461 10y ago
  Who cares about the key? It's not like the victim is gonna find it and reverse the cryptography himself. Hiding the key is unnecessary over engineering.
  - dmoy 10y ago
    If the key is accessible, someone could write software to automate breaking your ransomware.
- dmoy 10y ago
  That is generally how one encrypts large files with pk, yea. In fact I vaguely recall some crypto tool I had for personal use many years ago did exactly that for files above some size. The end result is you see a file encrypted with a symmetric key.
- jakobdabo 10y ago
  Yes, given a theoretical ransomware which uses AES and RSA I would assume it's operating like this (pseudo-code): private_key, public_key = keygen_rsa(); send_home(computer_id, private_key); wipe(private_key); for file in files { aes_iv = ivgen_aes() aes_key = keygen_aes() encrypted_file = aes_ccm_encrypt(file, aes_iv, aes_key); encrypted_aes_key = rsa_encrypt(aes_key, public_key); wipe(aes_key); filepos(file, 0); write(file, aes_iv); write(file, encrypted_aes_key); write(file, encrypted_file); }
  - aftbit 10y ago
    I'd guess something more like (ignoring IVs for now): aes_key = keygen_aes() crypted_aes_key = rsa_encrypt(MALWARE_PUB_KEY, aes_key) for file in files: content = read(file) encrypted = aes_encrypt(content, aes_key) write(file, encrypted) wipe(aes_key) display(RANSOM_NOTE, crypted_aes_key) I'd assume all the details needed to decrypt the files EXCEPT for a small key would be stored in the encrypted file headers. The AES key could be encrypted to a given public key and then directly displayed to the victim. This means that the software doesn't really need to know how to send infoto the ransomware writers. Instead the victim would be responsible for contacting them.
    - Cyph0n 10y ago
      Interesting idea! So for example, the user would provide the displayed hex digest as a note along with the payment. The payment verification server could then email the user the decrypted key.
      - aftbit 10y ago
        Yeah, or more likely a Bitcoin address and payment amount would be generated based on the attacker's Bitcoin public key and a hash of the encrypted key. Then the victim would pay that address and somehow contact the attacker (email, forum, twitter, whatever). The point is that the attacker could rely on the victim's human ingenuity to make it harder for the authorities to block payments.
- deleted 10y ago
  [deleted]
- omginternets 10y ago
  >Perhaps the AES key is encrypted with RSA after encryption is complete and kept on the infected machine. I think this is how PKE is usually done, precisely for the reasons you mention.

Cyph0n 10y ago

Using PK crypto would be horrendously slow, especially if there are a large number of files. Besides, the article notes that this ransomware uses AES-256. Perhaps the AES key is encrypted with RSA after encryption is complete and kept on the infected machine.

user5994461 10y ago
Who cares about the key? It's not like the victim is gonna find it and reverse the cryptography himself. Hiding the key is unnecessary over engineering.
- dmoy 10y ago
  If the key is accessible, someone could write software to automate breaking your ransomware.
dmoy 10y ago
That is generally how one encrypts large files with pk, yea. In fact I vaguely recall some crypto tool I had for personal use many years ago did exactly that for files above some size. The end result is you see a file encrypted with a symmetric key.
jakobdabo 10y ago
Yes, given a theoretical ransomware which uses AES and RSA I would assume it's operating like this (pseudo-code): private_key, public_key = keygen_rsa(); send_home(computer_id, private_key); wipe(private_key); for file in files { aes_iv = ivgen_aes() aes_key = keygen_aes() encrypted_file = aes_ccm_encrypt(file, aes_iv, aes_key); encrypted_aes_key = rsa_encrypt(aes_key, public_key); wipe(aes_key); filepos(file, 0); write(file, aes_iv); write(file, encrypted_aes_key); write(file, encrypted_file); }
- aftbit 10y ago
  I'd guess something more like (ignoring IVs for now): aes_key = keygen_aes() crypted_aes_key = rsa_encrypt(MALWARE_PUB_KEY, aes_key) for file in files: content = read(file) encrypted = aes_encrypt(content, aes_key) write(file, encrypted) wipe(aes_key) display(RANSOM_NOTE, crypted_aes_key) I'd assume all the details needed to decrypt the files EXCEPT for a small key would be stored in the encrypted file headers. The AES key could be encrypted to a given public key and then directly displayed to the victim. This means that the software doesn't really need to know how to send infoto the ransomware writers. Instead the victim would be responsible for contacting them.
  - Cyph0n 10y ago
    Interesting idea! So for example, the user would provide the displayed hex digest as a note along with the payment. The payment verification server could then email the user the decrypted key.
    - aftbit 10y ago
      Yeah, or more likely a Bitcoin address and payment amount would be generated based on the attacker's Bitcoin public key and a hash of the encrypted key. Then the victim would pay that address and somehow contact the attacker (email, forum, twitter, whatever). The point is that the attacker could rely on the victim's human ingenuity to make it harder for the authorities to block payments.
deleted 10y ago
[deleted]
omginternets 10y ago
>Perhaps the AES key is encrypted with RSA after encryption is complete and kept on the infected machine. I think this is how PKE is usually done, precisely for the reasons you mention.