> For the complete documentation index, see [llms.txt](https://docs.payments.thalescloud.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.payments.thalescloud.io/nfc-wallet-sdk-android/help/knowledge-base/compute-the-application-binding-key.md). # Compute the application binding key ## Overview In **NFC Wallet**, the Android **application binding key** is the `signer public key SHA-256 digest`. It is the SHA-256 hash of the signer **public key** extracted from the application signing certificate. Retrieve the `signer public key SHA-256 digest` using one of the options below, then share the resulting hex value with the **Thales delivery team.** This restricts NFC Wallet usage to a registered **digital wallet application**. {% hint style="info" %} You might need to share multiple values if your signing setup differs per environment (for example: **PreProd**, **Production**). {% endhint %} Share the hash exactly as printed. Do not add separators or spaces. Pick the option that matches your signing setup. See [Android app signing](https://developer.android.com/studio/publish/app-signing) for background. ## Option 1: Inspect the signed application package This is the simplest option. You need access to the signed APK on a workstation. For **Production**, you often install the app from Google Play, then [pull the APK from a test device](https://stackoverflow.com/questions/4032960/how-do-i-get-an-apk-file-from-an-android-device). You also need `apksigner` from the Android SDK Build Tools. Example location: `%ANDROID_HOME%\build-tools\33.0.1\`. Once the application package is available its signature could be examined with a single command. For example: ```nushell apksigner verify -v --print-certs Sample-sandbox-debug.apk Verifies Verified using v1 scheme (JAR signing): false Verified using v2 scheme (APK Signature Scheme v2): true Verified using v3 scheme (APK Signature Scheme v3): false Verified using v3.1 scheme (APK Signature Scheme v3.1): false Verified using v4 scheme (APK Signature Scheme v4): false Verified for SourceStamp: false Number of signers: 1 Signer #1 certificate DN: CN=D1 Signer #1 certificate SHA-256 digest: 591411c6efdc32c0a48ebf023583af589a50fd34914b9277377954ecff91b325 Signer #1 certificate SHA-1 digest: 2829a0da71747ae11cce49e77a361267f1abf58d Signer #1 certificate MD5 digest: d14c33afe4217372edfa4eea92ede878 Signer #1 key algorithm: RSA Signer #1 key size (bits): 2048 Signer #1 public key SHA-256 digest: b8e36f1efe7e4c827aeb390fafbf500d971c7e09a0bb62f84cfbaf8e0c770496 Signer #1 public key SHA-1 digest: 3df52267537eebfed228f704af7ab02e54f47172 Signer #1 public key MD5 digest: 97fb0a170b1499956ead185500ea3738 ``` Use the value from `Signer #1 public key SHA-256 digest`. In the example above, share: `b8e36f1efe7e4c827aeb390fafbf500d971c7e09a0bb62f84cfbaf8e0c770496` ## Option 2: Retrieve from a local Java keystore file The examples below use a Thales **PreProd** keystore shipped with the Training App. Use your own signing keys for **Sandbox**, **PreProd**, and **Production**. ### Step 1: Inspect the keystore file Using a [Java keytool](https://docs.oracle.com/javase/8/docs/technotes/tools/unix/keytool.html) utility, you can inspect the keystore file as follows: ```nushell keytool -v -list -keystore ``` Example:

Example: keytool -list output for the keystore

### Step 2: Extract the public key certificate The Java keytool is used again to extract a public key certificate for the particular key entry identified by the alias. Command: ```nushell keytool -export -alias -keystore -rfc -file ``` Example: ```nushell c:\Temp>keytool -export -alias gto -keystore release.keystore -rfc -file public.cert Enter keystore password: Certificate stored in file ``` ### Step 3: Get the hash If Thales provided `PKPinGenerator.jar`, use it to generate the public key hash. Command: ```nushell java -jar PKPinGenerator.jar ``` Example: ```sh c:\Temp>java -jar PKPinGenerator.jar public.cert ************************************************** ** Public Key Hash Generator ** ************************************************** Public Key Hash #1: E7F85A18D065DF41A3DD59ECB5FF5807CACABAE8DFACCDE12DB24BD658299C54 ``` Share the hash printed in the output. In this example: `E7F85A18D065DF41A3DD59ECB5FF5807CACABAE8DFACCDE12DB24BD658299C54` ## Option 3: Retrieve from the Google Play app signing certificate **Step 1: Download the certificate from Google Play Console**

Download the app signing certificate from Google Play Console

**Step 2: Extract the public key and its hash** There are various ways to achieve the same result, but it is recommended to use the following sequence of commands using [OpenSSL](https://www.openssl.org/): ```sh openssl x509 -in deployment_cert.der -inform DER -out deployment_cert.crt openssl x509 -noout -in deployment_cert.crt -pubkey | openssl asn1parse -noout -inform pem -out deployment_cert.key openssl dgst -sha256 -hex deployment_cert.key SHA256(deployment_cert.key)= [public key hash to share with Thales] ``` --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.payments.thalescloud.io/nfc-wallet-sdk-android/help/knowledge-base/compute-the-application-binding-key.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.