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Sign here, please!

Sign here, please!

An application ID might define your app among all others, but its signature is what proves and confirms its identity and integrity. From working in distributed teams to fending off fraudulent clones of your application, you eventually come to understand the importance of signatures.

In this talk we’ll take a deep dive into the Android keystore system, certificates and signatures, and go over key points necessary for any application’s long and productive life. Also, we will cover some security tips and tricks that will help ensure your app is safe to use, even if the users are faced with its evil twin.

At the end you should walk away with a deeper insight into everyday mechanisms that are often taken for granted, and the impact that they have on your users’ security.

Ana Baotić

March 26, 2018
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  1. SIGN HERE, PLEASE!
    ANA BAOTIĆ @abaotic

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  2. Present in

    54

    countries
    Over
    22,300

    highly committed
    employees
    6th

    largest software
    & services
    vendor in Europe
    1,813

    m EUR
    sales revenues in
    2016
    176

    m EUR
    operating profit
    in 2016
    1bln

    EUR
    market
    capitalization
    • Founded in 1991
    • 6th largest software producer in Europe
    • Traded on the WSE, included in the WIG20 blue chip
    index
    • International presence
    ASSECO at a glance

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  3. CERTIFICATE
    Electronic document that
    proves ownership of a public key
    X.509 - structure
    TLS/SSL, electronic signatures
    CERTIFICATE

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  4. IDENTITY
    CERTIFICATE

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  5. PUBLIC KEY
    CERTIFICATE = IDENTITY +
    +

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  6. SIGNED BY CA
    CERTIFICATE = IDENTITY + PUBLIC KEY
    +
    +

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  7. KEYS
    ASYMMETRIC CRYPTOGRAPHY

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  8. KEYS
    ▸ Private (owner)
    ▸ Decrypts messages
    ▸ Calculates signatures
    ▸ Public (shared)
    ▸ Encrypts messages
    ▸ Confirms signatures

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  9. DIGITAL SIGNATURE
    ▸ Calculate a digest/hash of the message
    ▸ Sender encrypts with private key
    ▸ Recipient decrypts with public key
    DIGITAL SIGNATURE

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  10. CERTIFICATE = IDENTITY + PUBLIC KEY + SIGNED BY CA
    +
    +

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  11. CERTIFICATE AUTHORITY
    CA
    Trusted entity that issues digital certificates.

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  12. CA
    CA CERTIFICATE
    ▸ Self-signed certificate
    ▸ Browsers, Android, OSX
    ▸ Comodo, IdenTrust, Symantec, GoDaddy, Let’s Encrypt
    ▸ Impact of updates!

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  13. CA - DOMAIN VS EXTENDED VALIDATION

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  14. END CERTIFICATE

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  15. INTERMEDIATE CERTIFICATE

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  16. ROOT CERTIFICATE

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  17. CERTIFICATES
    CERTIFICATE CHAINS

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  18. CA
    SUBVERSION
    ▸ Primary risk key theft
    ▸ Scheme flawed
    ▸ HSM for key storage
    ▸ Offline

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  19. TRUST
    ANDROID
    ▸ Unknown CA
    ▸ Self-signed
    ▸ No intermediate cert on server

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  20. SIGNING ANDROID APPLICATIONS

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  21. SIGNING ANDROID APPLICATIONS
    ▸ Generate a key and keystore
    ▸ Sign your application

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  22. SIGNING ANDROID APPLICATIONS - NEW KEY STORE

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  23. SIGNING ANDROID APPLICATIONS - SIGN THE APP

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  24. SIGNING ANDROID APPLICATIONS - SIGN THE APP
    ALTERNATIVE
    ▸ keytool to generate a key
    ▸ zipalign to align unsigned apk
    ▸ jarsigner to sign aligned apk

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  25. SIGN THE APK
    DECISIONS TO BE MADE
    ▸ Who will be responsible for the signing key?

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  26. WE THE DEVELOPERS

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  27. WE THE DEVELOPERS
    EXPECTATIONS
    ▸ Application can be updated throughout its lifetime

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  28. WE THE DEVELOPERS
    PREREQUISITES
    ▸ Signing key must be safe
    ▸ Signing key must be accessible

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  29. WE THE DEVELOPERS
    REALITY
    ▸ People spill coffee
    ▸ People switch companies

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  30. WE THE DEVELOPERS
    REALITY NIGHTMARE
    signingConfigs {
    release {
    storeFile file("/not_where_you_think_it_is/ks.jks")
    storePassword "password"
    keyAlias "my-alias"
    keyPassword "password"
    }
    }

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  31. GOOGLE PLAY APP SIGNING
    https://goo.gl/3aCBeC

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  32. GOOGLE PLAY APP SIGNING
    DECISION IS PERMANENT

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  33. GOOGLE PLAY APP SIGNING
    NEW APPS
    ▸ Create upload key and sign apk
    ▸ Google Play App Signing ->Accept
    ▸ Upload signed apk
    ▸ Register app signing key!

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  34. GOOGLE PLAY APP SIGNING
    EXISTING APPS
    ▸ Opt-in
    ▸ Submit signing key to Google and
    ▸ Create upload key
    ▸ Update keystores
    ▸ Continue signing with upload key

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  35. WE THE DEVELOPERS
    MITIGATION
    ▸ Upload key lost/compromised?

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  36. SIGN THE APK
    DECISIONS TO BE MADE
    ▸ Who will be responsible for the signing key?
    ▸ Applicable to all modules/applications/flavours?

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  37. SIGN THE APK
    PROS AND CONS
    ▸ Modularity
    ▸ Permission based
    sharing
    ▸ update-able
    ▸ Single point of failure

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  38. ANDROID KEYSTORE SYSTEM

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  39. ANDROID KEYSTORE SYSTEM
    The Android Keystore system safeguards your
    cryptographic keys from extraction.
    ANDROID KEYSTORE SYSTEM

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  40. STORAGE
    SHOULD I KEEP SENSITIVE DATA IN MY APP?

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  41. ANDROID KEYSTORE SYSTEM
    EXTRACTION PREVENTION
    ▸ System process in charge of cryptographic operations
    ▸ Key material bound to TEE, SE

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  42. ANDROID KEYSTORE SYSTEM
    KEY USE AUTHORIZATIONS
    ▸ Once defined, immutable
    ▸ Cryptography
    ▸ Temporal validity interval
    ▸ User authentication

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  43. ANDROID KEYSTORE SYSTEM
    UTILITY METHODS
    ▸ KeyInfo.isInsideSecurityHardware()
    ▸ KeyInfo.isUserAuthenticationRequirementEnforcedBySecureHardware()

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  44. ANDROID KEYSTORE SYSTEM
    KEYCHAIN VS ANDROID KEYSTORE PROVIDER
    ▸ System-wide credentials
    ▸ System provided UI
    ▸ App-specific credentials
    ▸ No interaction
    ▸ AndroidKeystore API 18

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  45. KEY PAIR ENTRY IN KEYSTORE
    KeyPairGenerator kpg = KeyPairGenerator.getInstance(
    KeyProperties.KEY_ALGORITHM_EC, "AndroidKeyStore");
    kpg.initialize(new KeyGenParameterSpec.Builder(
    alias,
    KeyProperties.PURPOSE_SIGN | KeyProperties.PURPOSE_VERIFY)
    .setDigests(KeyProperties.DIGEST_SHA256,
    KeyProperties.DIGEST_SHA512)
    .build());
    KeyPair kp = kpg.generateKeyPair();

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  46. KEY PAIR ENTRY IN KEYSTORE
    KeyPairGenerator kpg = KeyPairGenerator.getInstance(
    KeyProperties.KEY_ALGORITHM_EC, "AndroidKeyStore");
    kpg.initialize(new KeyGenParameterSpec.Builder(
    alias,
    KeyProperties.PURPOSE_SIGN | KeyProperties.PURPOSE_VERIFY)
    .setDigests(KeyProperties.DIGEST_SHA256,
    KeyProperties.DIGEST_SHA512)
    .build());
    KeyPair kp = kpg.generateKeyPair();

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  47. KEY PAIR ENTRY IN KEYSTORE
    KeyPairGenerator kpg = KeyPairGenerator.getInstance(
    KeyProperties.KEY_ALGORITHM_EC, "AndroidKeystore");
    kpg.initialize(new KeyGenParameterSpec.Builder(
    alias,
    KeyProperties.PURPOSE_SIGN | KeyProperties.PURPOSE_VERIFY)
    .setDigests(KeyProperties.DIGEST_SHA256,
    KeyProperties.DIGEST_SHA512)
    .build());
    KeyPair kp = kpg.generateKeyPair();

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  48. LISTING ENTRIES
    KeyStore ks = KeyStore.getInstance("AndroidKeyStore");
    ks.load(null);
    Enumeration aliases = ks.aliases();

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  49. LISTING ENTRIES
    KeyStore ks = KeyStore.getInstance("AndroidKeyStore");
    ks.load(null);
    Enumeration aliases = ks.aliases();

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  50. SIGNING DATA
    Signature s = Signature.getInstance("SHA256withECDSA");
    s.initSign(((PrivateKeyEntry) entry).getPrivateKey());
    s.update(data);
    byte[] signature = s.sign();

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  51. SIGNING DATA
    Signature s = Signature.getInstance("SHA256withECDSA");
    s.initSign(((PrivateKeyEntry) entry).getPrivateKey());
    s.update(data);
    byte[] signature = s.sign();

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  52. VERIFYING SIGNATURES
    Signature s = Signature.getInstance("SHA256withECDSA");
    s.initVerify(((PrivateKeyEntry) entry).getCertificate());
    s.update(data);
    boolean valid = s.verify(signature);

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  53. VERIFYING SIGNATURES
    Signature s = Signature.getInstance("SHA256withECDSA");
    s.initVerify(((PrivateKeyEntry) entry).getCertificate());
    s.update(data);
    boolean valid = s.verify(signature);

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  54. KEY ATTESTATION
    KEY ATTESTATION
    ▸ Is a key stored in hardware-backed keystore
    ▸ Small number of devices API 24+

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  55. FRAGMENTATION
    ANDROID P(ANCAKE?)
    ▸ Key rotation
    ▸ StrongBox Keymaster (HSM)
    ▸ …

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  56. GOOGLE TRANSPARENCY REPORT
    https://transparencyreport.google.com/

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  57. QUALYS
    CHECK YOUR DOMAIN (NOW!)
    https://www.ssllabs.com/ssltest/analyze.html

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  58. THANK YOU!
    Q&A

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