Re:Postbank to replace 12M bank cards after employees steal ...
by motohagiography on Wednesday June 17, 2020 @02:22PM
(#23554817)
While the details are sparse, in card payments, you typically use an HSM and provision keys to card blanks using the EMV "personalization" protocol. It derives a bunch of keys from the master secret, and the whole chain of trust is based on these key derivations. These are symmetric keys/secrets, since most chip cards don't have the processing power for RSA, and ECC is still too recent for some of these legacy payment systems.
What it means is that the master secret in the HSM is probably a 128bit AES key. The ways to generate this depend on the ceremony and the particular HSM, but the risk I have encountered in security consulting is the question of whether that master secret itself was just derived from simple components, like pbkdf2("secret phrase known to 3 people", 1000)
The consequence of compromising that key is that an attacker could use it to forge cards, or more usefully, instantiate a virtual card in software to fuzz cryptograms for different account numbers to get available balance information and then personalize cards for those.
What it means is that the master secret in the HSM is probably a 128bit AES key. The ways to generate this depend on the ceremony and the particular HSM, but the risk I have encountered in security consulting is the question of whether that master secret itself was just derived from simple components, like pbkdf2("secret phrase known to 3 people", 1000)
The consequence of compromising that key is that an attacker could use it to forge cards, or more usefully, instantiate a virtual card in software to fuzz cryptograms for different account numbers to get available balance information and then personalize cards for those.