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PIN entry on Tap to Phone solutions, because of its very sensitive nature, is handled by the Secure Client (and the Secure Backend). The flow is relatively simple, the PIN prompt is triggered by one API call. The output of the PIN entry is provided through a callback.
The following figure describes the message flow between the different merchant’s system components involved in the online PIN verification process:
For security reasons, the PAN (card data), returned by the L2/OLA API and the partial PIN block, returned by SCSDK PIN pad are encrypted using two different key set in two independent key spaces, named security domains (identified as PIN and PAN).
It is the role of the merchant’s system to transmit and use the PIN and PAN cryptograms for computing the standard PIN block in a secure environment. The resulting PIN block is used in the actual online PIN verification.
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PIN prompt
To launch the PIN entry screen, once must call the pinEnter() method from the AOneAppSecurity class as follows:
| Code Block |
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AOneAppSecuritySecureClient.getInstance(this.contextactivity, AOneAppSecurityCbk(this.activity)) .pinEnter(activity, amount, message, min, max, timeout, feedback) |
With:
amount: the amount string, including currency (ex: $ 51.00)
message: the customer message (ex: Please enter PIN)
min: the minimum number of PIN digits (usually 4)
max: the maximum number of PIN digits
timeout: the PIN entry timeout in secondsfeedback: physical and audible feedback flags (ex:
AOneAppSecurity.PIN_ENTRY_FB_HAPTIC or AOneAppSecurity.PIN_ENTRY_FB_SOUND)
| Info |
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Once the |
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The format of the partial PIN block cryptogram is:
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E(PIN block) = ID(Kpin-pub)||ERSA-OAEP-SHA-1(Kpin-pub, Kpin-session)||Eaes-ecb(Kpin-session, pin-block)
Which translates into:
| Note |
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The format of the PIN block cryptogram changed staring secure client v1.0.9 |
Object | Length (bytes) | Comments |
|---|---|---|
RSA Key ID 5length | 2 | Length of the key ID (MSB) |
RSA Key ID | var | RSA key ID used for the session key encryption |
Encrypted KEK length | 2 | Length of the encrypted KEK (MSB - should be 512) |
Encrypted KEK | 256512 | Encrypted KEK block:
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Encrypted pseudo PIN block 256length | 2 | Length of the encrypted PIN block (MSB - should be 16) |
Encrypted pseudo PIN block | 16 | Encrypted pseudo PIN block:
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HMAC Key ID length | 2 | Length of the HMAC key ID (MSB) |
HMAC Key ID | var | HMAC key ID used for the checksum calculation |
HMAC length | 2 | Length of the HMAC checksum (MSB - should be 32) |
HMAC | 32 | AES-CBC-256 checksum |
The pseudo PIN block is encoded in ISO-0 format, with the PIN set as expected and the PAN set to “F…F”:
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Object
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Length (bytes)
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the following way:
If N is the number of PIN digits, with N in the [4, 12] range, the PIN is encoded in a 16 bytes byte array with the following format:
A prefix of (16 - N) random bytes Bi:
B0 … B(16 - N - 2) = 0xmn where m and n denote the most and least significant nibbles
B(16 - N - 1) = 0xm0, end of prefix
The encoded PIN of N bytes, each byte encoding a PIN digit:
B0(16 - N) … B15 = 0xmd where m(random) and d(PIN digit) denote the most and least significant nibbles
The following table gives an example of the encoding of the encoding of the PIN value “1234”:
0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
0xB9 | 0x6F | 0x4A | 0x31 | 0x06 | 0x9E | 0x73 | 0x48 | 0x9A | 0xA7 | 0xD3 | 0x60 | 0xD1 | 0x62 | 0xE3 | 0xD4 |