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@ -146,8 +146,63 @@ networks, almost all payment terminals on the market irrespective of their count
standards. Adding on to PCI's ecosystem impact, its security standards are thought out well and provide a higher level
of security than one might expect from an industry association.
The concrete requirements in the PCI SSC standards boil down to a list of logical requirements regarding key handling
that
Physical security standards in card payment applications both on the client side -- payment terminals -- and on the
server side -- HSM appliances -- are more stringent than one might expect since the finance industry has been reluctant
to adopt modern cryptography. Not only are modern cryptographic protocols like Secure Multiparty Computation (SMPC) or
Zero-Knowledge Proofs (ZKPs) not commonly used. Even asymmetric cryptography has only been adopted reluctantly, and
ancient ciphers such as Triple DES are still commonly referenced in industry
standards~\cite{pci_security_standards_council_payment_2025}. As a result, increased hardware security is necessary to
safeguard weak symmetric keys, compensating for the systems' modest cryptographic security.
Since card payment terminals are widely deployed, many different models from various manufacturers are available. Each
manufacturer tends to have their own, patented tamper-sensing implementation. Being manufactured at scale, card payment
terminals are cost-sensitive devices, which is reflected in the construction of their tamper-sensing implementations.
\subsubsection{HSM Appliances}
For datacenter applications, HSMs are sold both as add-in cards and as standalone rackmount appliances with a network
interface. In practice, the standalone appliances are just low-end computers in a rackmount enclosure that expose the
API of an internal HSM add-in card to the network. In this survey, we were only able to procure a single such HSM since
these devices are expensive, and even used specimens of older models are usually listed for several hundreds to several
thousands of EUR. The one sample we procured was a 2011 model Utimaco CryptoServer LAN. Our unit was a white-label
variant procured by premium TV encryption technology provider Irdeto, presumably used in Germany to produce
cryptographic key streams for TV signal encryption. We bought the device from a recycling company specialized on
datacenter components. The device was sold with any HDDs removed. The device consisted of an older mainboard for
embedded applications containing an Intel Core 2 Duo-brand processor and 2 GiB of DDR2 RAM, which was connected to the
HSM add-in card through PCI. The device contained a small Lithium backup battery on the add-in card, and another, larger
battery in an enclosure at the front of the device that was connected to the card through a cable. The device did not
contain any obvious case intrusion sensors.
\subsubsection{ATM Encrypting Pin Pads}
ATMs are built in a modular construction approach. Physically, the enclosure of an ATM is not its only security
barrier. Besides the enclosure, there are two security barriers worthy of note. First, the bank notes in the machine are
stored in an automatic cash dispenser that is built into a traditional vault inside the machine. This vault primarily
acts as a mechanical barrier to discourage theft, but it also often includes tamper sensors that activate an Intelligent
Banknote Neutralisation System (IBNS). The IBNS is designed to spread hard-to-remove ink over the bank notes inside the
vault when tampered. The permanently stained bank notes are not accepted by banks or retailers anymore.
% FIXME cite https://www.oberthurcp.com/hubfs/Oberthur_December2020/Pdf/IBNS_Introduction_to_ink_staining_Oberthur_Cash_Protection_2019.pdf
% archive: https://web.archive.org/web/20250822134238/https://www.oberthurcp.com/hubfs/Oberthur_December2020/Pdf/IBNS_Introduction_to_ink_staining_Oberthur_Cash_Protection_2019.pdf
% FIXME cite https://www.ecb.europa.eu/euro/banknotes/damaged/html/index.en.html
% FIXME cite https://www.bcl.lu/en/Banknotes-and-Coins/remboursement/billets-macules1/index.html
Besides the vault, the other secondary security barrier is located inside the ATM's pin pad. While all communication
with the customer's card passes through an end-to-end encrypted channel from the bank's backends into the card's
smartcard IC, the customer must necessarily enter their pin in plain text. To prevent leakage of the plaintext PIN, the
PIN is encrypted inside the PIN pad itself. To this end, the PIN pad contains a microcontroller handling the encryption.
Often, both the circuit board containing the PIN pad's keyboard matrix and this microcontroller are shielded by a
tamper-sensing mesh to prevent physical attacks such as the installation of a skimming device that would record and
transmit the plaintex PIN.
We acquired three different EPPs for analysis: Two designed by Sagem and apparently re-sold as a whitelabel product by
Cryptera and Diebold, respectively, and one made by and branded NCR. All three devices have robust stainless steel front
cases.
\subsubsection{Other miscellaneous devices}
Sometimes, tamper-sensing meshes show up in other types of devices. We acquired two such devices. First, we acquired a
Neopost franking machine, a type of device that is used to directly print a code on an envelope that replaces a
conventional postage stamp.
\section{Conclusion}