2 years ago I found out that if you order a SwissPass, they will gladly send it to your address for free, anywhere in the world. Since a lot of my friends and I collect funny transport cards, we immediately got some ordered for ourselves.

I was mostly using it as it was intended, loading my short-time tickets from the ZVV on it when I was in Zürich and using EasyRide in the SBB app (since it requires a card to be issued). I knew that the card supported more features (as they are even advertised on their website), but wasn’t really interested in looking deeper into them. This changed recently, when I finally decided to take a crack at it.

Initial discoveries

I started by looking into what kind of identifiers the card uses. SBB ticket machines seem to use the barcode or QR code with the card ID on the back, while most other ticket machines seem to use the ISO 14443 UID that is read via NFC. Since the card also shows an RFID logo, I was interested. Initial discoveries with my Proxmark 3 showed 2 different chips inside the card (UIDs redacted).

[usb] pm3 --> hf search
 🕗 Searching for ISO14443-A tag...           
[=] ---------- ISO14443-A Information ----------
[+]  UID: 04 XX XX XX XX XX 90   ( double )
[+] ATQA: 00 48
[+]  SAK: 20 [1]
[+]       NXP Semiconductors Germany
[+] Possible types:
[+]    EMV
[=] -------------------------- ATS ----------------------------------
[+] ATS: 0E 78 80 71 02 53 77 69 73 73 50 61 73 73 [ 35 EE ]
[=]      0E...............  TL    length is 14 bytes
[=]      ...78............  T0    TA1 is present, TB1 is present, TC1 is present, FSCI is 8 (FSC = 256)
[=]      ......80.........  TA1   different divisors are NOT supported, DR: [], DS: []
[=]      .........71......  TB1   SFGI = 1 (SFGT = 8192/fc), FWI = 7 (FWT = 524288/fc)
[=]      ............02...  TC1   NAD is NOT supported, CID is supported

[=] -------------------- Historical bytes ---------------------------
[+] 537769737350617373 - SwissPass

[=] ------------------ ATR fingerprinting ---------------------------
[+]     SwissPass - key to mobility and leisure in Switzerland (Transport)
[+]     https://www.swisspass.ch
[+]     https://www.allianceswisspass.ch/de/informationen-ov-nutzende/SwissPass

[?] Hint: Try `emv reader`


[+] Valid ISO 14443-A tag found

[?] Hint: Try `hf fido` commands
[?] Hint: Try `emv` commands
 🕕 Searching for ISO15693 tag...             
[+] UID.... E0 XX XX XX XX XX XX EA
[+] DSFID.. 02
[+] TYPE MATCH EM-Marin SA (Skidata); EM4237 [IC id = 15] 23,5pF

[+] Valid ISO 15693 tag found

[?] Hint: Try `hf 15` commands

The tale of two chips

The ISO 15693 chip seems to be a factory fresh reloadable SKIDATA card, which I confirmed by some sectors matching those that other people found. As I don’t ski, I wasn’t particularly interested in this one.

The ISO 14443 chip seemed to be much more powerful though, claiming it included an EMV and a FIDO applet (which is also noted on the official website). I also scanned the card with NXP TagInfo on my Pixel 9 (after finding the button to disable the ISO 15693 reading as it kept conflicting). The app showed that the card had a Global Platform card manager, PPSE (contactless payments) and 4 applets named SwissPass, Legic, Mastercard and FIDO. I also confirmed this with my Proxmark.

[usb] pm3 --> emv pse -st2
[=] Selected channel... CONTACTLESS (T=CL)
[=] APDU response status: 9000 - Command successfully executed (OK).
[=] -------------------- TLV decoded --------------------
[=]  --6f[76] 'File Control Information (FCI) Template':
[=]     --84[0e] 'Dedicated File (DF) Name':
[=]     00: 32 50 41 59 2E 53 59 53 2E 44 44 46 30 31       | 2PAY.SYS.DDF01
[=]     --a5[64] 'File Control Information (FCI) Proprietary Template':
[=]         --bf0c[61] 'File Control Information (FCI) Issuer Discretionary Data':
[=]             --61[1a] 'Application Template':
[=]                 --4f[0a] 'Application Dedicated File (ADF) Name':
[=]                 00: A0 00 00 06 26 01 01 01 00 01                   | �...&.....
[=]                 --50[09] 'Application Label':    String value '537769737350617373'
[=]                 00: 53 77 69 73 73 50 61 73 73                      | SwissPass
[=]                 --87[01] 'Application Priority Indicator':
[=]                 00: 01                                              | .
[=]             --61[13] 'Application Template':
[=]                 --4f[07] 'Application Dedicated File (ADF) Name':
[=]                 00: A0 00 00 03 57 00 00                            | �...W..
[=]                 --50[05] 'Application Label':    String value '4C65676963'
[=]                 00: 4C 65 67 69 63                                  | Legic
[=]                 --87[01] 'Application Priority Indicator':
[=]                 00: 02                                              | .
[=]             --61[18] 'Application Template':
[=]                 --4f[07] 'Application Dedicated File (ADF) Name':
[=]                 00: A0 00 00 00 04 10 10                            | �......
[=]                 --50[0a] 'Application Label':    String value '4D617374657263617264'
[=]                 00: 4D 61 73 74 65 72 63 61 72 64                   | Mastercard
[=]                 --87[01] 'Application Priority Indicator':
[=]                 00: 03                                              | .
[=]             --61[14] 'Application Template':
[=]                 --4f[08] 'Application Dedicated File (ADF) Name':
[=]                 00: A0 00 00 06 47 2F 00 01                         | �...G/..
[=]                 --50[05] 'Application Label':    String value '4649444F32'
[=]                 00: 46 49 44 4F 32                                  | FIDO2
[=]                 --87[01] 'Application Priority Indicator':
[=]                 00: 04                                              | .

My SwissPass is a Mastercard??

I was first surprised by the Mastercard applet, so I wanted to know more about it. Reading the PAN of the card, it started with the BIN of 223119, issued to Worldline Schweiz AG for a MASTERCARD PREPAID NON US GENERAL SPEND. The applet says it is valid for 5 years from the issue of the card. It is also very limited, only permitting transactions in Swiss Franc with an online PIN validation. As I was going to Bern soon for the Open Transport Conference, I activated the payment function on my SwissPass here and loaded up 20 CHF.

The first time I got to a ticket machine, I touched my SwissPass to the EMV terminal when payment was due and it asked me for my PIN (that I set online during activation) and it surprisingly (to me) went through. During the week, I learned it is accepted a lot more than just ticket machines. I was able to use my SwissPass on the station vending machines for example. This is definitely an interesting concept and I like that they used an existing network for this instead of relying on a homebrewed solution for payments.

Figuring out the SwissPass applet

My next target was the SwissPass applet. The RID of the applet is registered to SwissPass, so it must be the transport function of the card. Looking online, I found an article when the original SwissPass was made that describes the functioning of it. Apparently the card uses EC cryptography and includes a certificate with a “medium ID”. This is definitely something we would be interested in. Looking further, I also found a paper that apparently used these certificates as an authentication method for 2FA.

Just use brute force?

This made me wonder what the best approach would be to try figuring out how the applet worked. None of the paper code was public and I couldn’t find APDU specifications anywhere online. My next option was trying a spray-and-pray by just throwing all CLA and INS combinations at the card. Thankfully, the applet uses proper response codes for “CLA not supported” and “INS not supported”, so I could easily discard entire command classes.

By running the enumeration script, I found out the applet responds to 3 CLA/INS combinations, 80 01, A0 01 and A0 02. 80 01 00 00 responded with 02 04 01 00 00 00, probably a version, A0 01 00 00 responded with just 00 93 and interestingly, A0 02 00 00 responded with 67 00 as the response code, indicating Wrong length. This meant A0 02 00 00 might be the challenge-response command.

By trying different command payloads, I found out that the first byte of the payload is a bitmask of commands for the applet (multiple flags can be set, returning a bigger response).

Flag	Command
`0x01`	Sign challenge (data is after command byte)
`0x02`	Read Medium ID
`0x04`	Read Compressed P-256 public key
`0x08`	Read Compact certificate

The result is a custom TLV with a 1-byte tag and 1-byte length indicator.

Tag	Value
`0x01`	ECDSA signature of challenge
`0x03`	Compact certificate
`0x04`	Medium ID
`0x05`	Compressed P-256 public key

Figuring this out also explained the return of A0 01, which is the length of the certificate.

The “insane” certificate format

The compact certificate is made up of the following components (x indicates the length specified in the previous element):

Length	Field
1	Version (should be `02`)
16	Medium ID
1	Issuer name length
x	Issuer name (should be `SwissPass_CA_1`)
5	Valid from: unsigned big-endian Unix seconds
5	Valid to: unsigned big-endian Unix seconds
1	Compressed public-key length
x	Compressed public key
1	Issuer signature length
x	DER-encoded issuer ECDSA signature

The ECDSA signature is not done over the compressed form, but instead over a reconstructed X.509 TBSCertificate from the data in the compressed certificate. The ASN.1 schema for the certificate follows.

TBSCertificate ::= SEQUENCE {
    version         [0] EXPLICIT Version v3,

    serialNumber    INTEGER <16-byte MediumID>,

    signature       SEQUENCE {
        OBJECT IDENTIFIER ecdsa-with-SHA256
    },

    issuer          SEQUENCE {
        SET {
            SEQUENCE {
                OBJECT IDENTIFIER commonName,
                UTF8String <issuerName>
            }
        }
    },

    validity        SEQUENCE {
        UTCTime <notBefore>,
        UTCTime <notAfter>
    },

    subject         SEQUENCE {
        SET {
            SEQUENCE {
                OBJECT IDENTIFIER commonName,
                UTF8String <32-char-uppercase-MediumID>
            }
        }
    },

    subjectPublicKeyInfo SEQUENCE {
        SEQUENCE {
            OBJECT IDENTIFIER id-ecPublicKey,
            OBJECT IDENTIFIER prime256v1
        },
        BIT STRING <04 || X(32) || Y(32)>
    }
}

The SwissPass_CA_1 public key that I recovered from the SwissPass cards I had access to is below.

-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEwHc4CcLWc6j6yFoa8vOvEx5TdD5e
QuoHaXuF1Tbg8t7wWB4k5YyhtgaBZLA+XJvuHIRVU2x6Ao+hRRlRua9VMw==
-----END PUBLIC KEY-----

This key has validated all SwissPass cards we have seen in the wild for now.

The challenge-response flow requires either a 32 or 64-byte challenge and returns an ECDSA-SHA256 signature of it with the card private key that can be validated with the public key in the certificate.

Quick Dip into FIDO

I also took a quick glance at the FIDO applet. Since we know how those work, I was only interested in the card-specific data like the AAGUID and the attestation certificate. The AAGUID of my SwissPass is 37fecf7b-87a6-a14e-befe-42ff4412fa27 and the attestation certificate is below. Surprisingly it seems to also be signed by the SwissPass CA we found from the card-specific certificate. It also appears that the AAGUID is not on the FIDO Alliance Metadata Service.

The Legic applet

The SwissPass also seems to hold a LEGIC advant applet. Since the LEGIC advant system has not been reverse engineered by anyone yet, it is very hard to figure out what the applet does. The CLA/INS enumeration did not bear any fruits. The one file I was able to read did indicate that the chip seems to be an NXP SmartMX3 P71 with JCOP4 though. There is one page that seems to mention the LEGIC applet on the SBB Business page, but it requires a phone call with SBB.

Future ideas

With this information, I am thinking of creating an access control reader that just performs the challenge response flow and uses the Medium ID as the primary key. I will hopefully post it on my GitHub soon. If anyone has other ideas to use, feel free to @ me on fedi if you need any help or run into problems.

Cracking open the SwissPass