Catching Crypto Secrets in Android Apps with Frida

fdciabdul3 hours ago

0 6 4 minutes read

You know that feeling when you’re staring at an Android app and wondering “what the hell is this thing doing with my data?” Well, today we’re going to pull back the curtain and see exactly how apps handle encryption, hashing, and all that crypto stuff that usually happens in the shadows.

Why This Matters

Think about it – every time you log into an app, make a payment, or send a message, there’s crypto happening behind the scenes. Some apps do it right, others… well, let’s just say they get creative in ways that would make security experts cry.

Whether you’re a pentester trying to find weak spots, a developer debugging your own app, or just someone who’s curious about what’s really going on under the hood, this guide will show you how to catch every single crypto operation an Android app makes.

Setting Up Your Lab

Before we dive in, let’s get everything ready. You’ll need a proper setup to make this work smoothly.

The Basics

First, make sure you’ve got Frida installed properly:

1 2	pip install frida-tools

You’ll also need a rooted Android device or an emulator. If you’re using an emulator, I recommend using something like Genymotion or the Android Studio emulator with a rooted image.

For the device setup:

# Check if Frida server is running on your device

adb shell ps | grep frida

# If not, push and run frida-server

adb push frida-server /data/local/tmp/

adb shell "chmod 755 /data/local/tmp/frida-server"

adb shell "/data/local/tmp/frida-server &"

Finding Your Target

List all the apps running on your device:

1 2	frida-ps -U

Or if you want to see all installed apps:

1 2	frida-ps -Ua

Understanding the Crypto Landscape

Android apps primarily use Java’s crypto APIs, which means they’re calling methods from packages like:

javax.crypto.* – For encryption, decryption, key generation
java.security.* – For hashing, signatures, key management
android.security.keystore.* – For hardware-backed key operations

Our script hooks into all of these, giving us a complete picture of what’s happening.

The Complete Tracing Script

Here’s the full script that does the heavy lifting. Save this as crypto_tracer.js:

function bin2ascii(array) {
    var result = [];
    for (var i = 0; i &lt; array.length; ++i) {
        result.push(String.fromCharCode(
            parseInt(
                ('0' + (array[i] &amp; 0xFF).toString(16)).slice(-2),
                16
            )
        ));
    }
    return result.join('');
}

function bin2hex(array, length) {
    var result = "";
    length = length || array.length;
    for (var i = 0; i &lt; length; ++i) {
        result += ('0' + (array[i] &amp; 0xFF).toString(16)).slice(-2);
    }
    return result;
}

setTimeout(function() {
    Java.perform(function() {
        console.log("[+] Crypto tracer started - hooking into crypto operations...");

var Log = Java.use("android.util.Log")
        var Exception = Java.use("java.lang.Exception")

// Hook KeyGenerator operations
        var keyGenerator = Java.use("javax.crypto.KeyGenerator");
        
        keyGenerator.generateKey.implementation = function() {
            console.log("[🔑] KeyGenerator.generateKey() called");
            console.log("    Algorithm: " + this.getAlgorithm());
            var result = this.generateKey();
            console.log("    Key generated successfully");
            return result;
        };

keyGenerator.getInstance.overload('java.lang.String').implementation = function(algorithm) {
            console.log("[🔑] KeyGenerator.getInstance() called");
            console.log("    Algorithm: " + algorithm);
            return this.getInstance(algorithm);
        };

keyGenerator.getInstance.overload('java.lang.String', 'java.lang.String').implementation = function(algorithm, provider) {
            console.log("[🔑] KeyGenerator.getInstance() called");
            console.log("    Algorithm: " + algorithm);
            console.log("    Provider: " + provider);
            return this.getInstance(algorithm, provider);
        };

// Hook SecretKeySpec - this is where we see actual key material
        var secretKeySpec = Java.use("javax.crypto.spec.SecretKeySpec");
        secretKeySpec.$init.overload('[B', 'java.lang.String').implementation = function(keyBytes, algorithm) {
            var key = Java.array('byte', keyBytes);
            console.log("[🗝️ ] SecretKeySpec created:");
            console.log("    Algorithm: " + algorithm);
            console.log("    Key (hex): " + bin2hex(key));
            console.log("    Key (ascii): " + bin2ascii(key));
            console.log("    Key length: " + key.length + " bytes");
            
            return secretKeySpec.$init.overload('[B', 'java.lang.String').call(this, keyBytes, algorithm);
        }

// Hook Cipher operations
        var cipher = Java.use("javax.crypto.Cipher");
        
        cipher.getInstance.overload('java.lang.String').implementation = function(transformation) {
            console.log("[🔐] Cipher.getInstance() called");
            console.log("    Transformation: " + transformation);
            return this.getInstance(transformation);
        };

cipher.init.overload('int', 'java.security.Key').implementation = function(opmode, key) {
            var mode = opmode == 1 ? "ENCRYPT" : opmode == 2 ? "DECRYPT" : "UNKNOWN(" + opmode + ")";
            console.log("[🔐] Cipher.init() called");
            console.log("    Mode: " + mode);
            console.log("    Algorithm: " + this.getAlgorithm());
            return this.init(opmode, key);
        };

cipher.init.overload('int', 'java.security.Key', 'java.security.spec.AlgorithmParameterSpec').implementation = function(opmode, key, params) {
            var mode = opmode == 1 ? "ENCRYPT" : opmode == 2 ? "DECRYPT" : "UNKNOWN(" + opmode + ")";
            console.log("[🔐] Cipher.init() called (with params)");
            console.log("    Mode: " + mode);
            console.log("    Algorithm: " + this.getAlgorithm());
            console.log("    Params: " + params);
            return this.init(opmode, key, params);
        };

cipher.doFinal.overload('[B').implementation = function(input) {
            console.log("[🔐] Cipher.doFinal() called");
            console.log("    Input length: " + input.length + " bytes");
            console.log("    Input (hex): " + bin2hex(Java.array('byte', input)));
            
            var result = cipher.doFinal.overload("[B").call(this, input);
            
            console.log("    Output length: " + result.length + " bytes");
            console.log("    Output (hex): " + bin2hex(Java.array('byte', result)));
            
            return result;
        };

// Hook MessageDigest (hashing)
        var messageDigest = Java.use("java.security.MessageDigest");
        
        messageDigest.getInstance.overload('java.lang.String').implementation = function(algorithm) {
            console.log("[🔒] MessageDigest.getInstance() called");
            console.log("    Algorithm: " + algorithm);
            return this.getInstance(algorithm);
        };

messageDigest.digest.overload().implementation = function() {
            console.log("[🔒] MessageDigest.digest() called");
            console.log("    Algorithm: " + this.getAlgorithm());
            
            var result = messageDigest.digest.overload().call(this);
            var hash = Java.array('byte', result);
            
            console.log("    Hash (hex): " + bin2hex(hash));
            console.log("    Hash length: " + hash.length + " bytes");
            
            return result;
        };

messageDigest.digest.overload('[B').implementation = function(input) {
            console.log("[🔒] MessageDigest.digest() called with input");
            console.log("    Algorithm: " + this.getAlgorithm());
            console.log("    Input length: " + input.length + " bytes");
            console.log("    Input (hex): " + bin2hex(Java.array('byte', input)));
            
            var result = messageDigest.digest.overload('[B').call(this, input);
            var hash = Java.array('byte', result);
            
            console.log("    Hash (hex): " + bin2hex(hash));
            
            return result;
        };

// Hook Mac (HMAC operations)
        var mac = Java.use("javax.crypto.Mac");
        
        mac.getInstance.overload('java.lang.String').implementation = function(algorithm) {
            console.log("[🔐] Mac.getInstance() called");
            console.log("    Algorithm: " + algorithm);
            return this.getInstance(algorithm);
        };

mac.init.overload('java.security.Key').implementation = function(key) {
            console.log("[🔐] Mac.init() called");
            console.log("    Algorithm: " + this.getAlgorithm());
            return this.init(key);
        };

mac.doFinal.overload().implementation = function() {
            console.log("[🔐] Mac.doFinal() called");
            console.log("    Algorithm: " + this.getAlgorithm());
            
            var result = mac.doFinal.overload().call(this);
            var hmac = Java.array('byte', result);
            
            console.log("    HMAC (hex): " + bin2hex(hmac));
            console.log("    HMAC length: " + hmac.length + " bytes");
            
            return result;
        };

// Hook Android Keystore operations
        var keyStore = Java.use("java.security.KeyStore");
        
        keyStore.getInstance.overload('java.lang.String').implementation = function(type) {
            console.log("[🏪] KeyStore.getInstance() called");
            console.log("    Type: " + type);
            return this.getInstance(type);
        };

keyStore.load.overload('java.io.InputStream', '[C').implementation = function(stream, password) {
            console.log("[🏪] KeyStore.load() called");
            if (password) {
                console.log("    Password length: " + password.length + " chars");
            }
            return this.load(stream, password);
        };

// Hook KeyGenParameterSpec for hardware-backed keys
        try {
            var keyGenBuilder = Java.use("android.security.keystore.KeyGenParameterSpec$Builder");
            
            keyGenBuilder.$init.overload("java.lang.String", "int").implementation = function(keystoreAlias, purposes) {
                var purposeStr = "";
                if (purposes &amp; 1) purposeStr += "ENCRYPT ";
                if (purposes &amp; 2) purposeStr += "DECRYPT ";
                if (purposes &amp; 4) purposeStr += "SIGN ";
                if (purposes &amp; 8) purposeStr += "VERIFY ";
                
                console.log("[🔐] KeyGenParameterSpec.Builder created");
                console.log("    Keystore alias: " + keystoreAlias);
                console.log("    Purposes: " + purposeStr + "(" + purposes + ")");
                
                return keyGenBuilder.$init.overload("java.lang.String", "int").call(this, keystoreAlias, purposes);
            };

keyGenBuilder.setKeySize.implementation = function(keySize) {
                console.log("[🔐] KeyGenParameterSpec: Key size set to " + keySize + " bits");
                return this.setKeySize(keySize);
            };

keyGenBuilder.setBlockModes.implementation = function(blockModes) {
                console.log("[🔐] KeyGenParameterSpec: Block modes: " + blockModes);
                return this.setBlockModes(blockModes);
            };

keyGenBuilder.setEncryptionPaddings.implementation = function(paddings) {
                console.log("[🔐] KeyGenParameterSpec: Encryption paddings: " + paddings);
                return this.setEncryptionPaddings(paddings);
            };
        } catch(e) {
            console.log("[!] KeyGenParameterSpec hooking failed (Android version might not support it)");
        }

// Hook IvParameterSpec to catch initialization vectors
        var ivSpec = Java.use("javax.crypto.spec.IvParameterSpec");
        
        ivSpec.$init.overload("[B").implementation = function(iv) {
            var ivArray = Java.array('byte', iv);
            console.log("[🔒] IvParameterSpec created");
            console.log("    IV (hex): " + bin2hex(ivArray));
            console.log("    IV (ascii): " + bin2ascii(ivArray));
            console.log("    IV length: " + ivArray.length + " bytes");
            
            return ivSpec.$init.overload("[B").call(this, iv);
        };

// Hook Signature operations
        var signature = Java.use("java.security.Signature");
        
        signature.getInstance.overload('java.lang.String').implementation = function(algorithm) {
            console.log("[✍️] Signature.getInstance() called");
            console.log("    Algorithm: " + algorithm);
            return this.getInstance(algorithm);
        };

signature.initSign.overload('java.security.PrivateKey').implementation = function(privateKey) {
            console.log("[✍️] Signature.initSign() called");
            console.log("    Algorithm: " + this.getAlgorithm());
            return this.initSign(privateKey);
        };

signature.initVerify.overload('java.security.PublicKey').implementation = function(publicKey) {
            console.log("[✍️] Signature.initVerify() called");
            console.log("    Algorithm: " + this.getAlgorithm());
            return this.initVerify(publicKey);
        };

signature.sign.overload().implementation = function() {
            console.log("[✍️] Signature.sign() called");
            console.log("    Algorithm: " + this.getAlgorithm());
            
            var result = signature.sign.overload().call(this);
            var sig = Java.array('byte', result);
            
            console.log("    Signature (hex): " + bin2hex(sig));
            console.log("    Signature length: " + sig.length + " bytes");
            
            return result;
        };

console.log("[+] All crypto hooks installed successfully!");
        console.log("[+] Waiting for crypto operations...");
    });
}, 0);

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function bin2ascii(array) {

var result = [];

for (var i = 0; i < array.length; ++i) {

result.push(String.fromCharCode(

parseInt(

('0' + (array[i] & 0xFF).toString(16)).slice(-2),

)

));

}

return result.join('');

}

function bin2hex(array, length) {

var result = "";

length = length || array.length;

for (var i = 0; i < length; ++i) {

result += ('0' + (array[i] & 0xFF).toString(16)).slice(-2);

}

return result;

}

setTimeout(function() {

Java.perform(function() {

console.log("[+] Crypto tracer started - hooking into crypto operations...");

var Log = Java.use("android.util.Log")

var Exception = Java.use("java.lang.Exception")

// Hook KeyGenerator operations

var keyGenerator = Java.use("javax.crypto.KeyGenerator");

keyGenerator.generateKey.implementation = function() {

console.log("[🔑] KeyGenerator.generateKey() called");

console.log(" Algorithm: " + this.getAlgorithm());

var result = this.generateKey();

console.log(" Key generated successfully");

return result;

};

keyGenerator.getInstance.overload('java.lang.String').implementation = function(algorithm) {

console.log("[🔑] KeyGenerator.getInstance() called");

console.log(" Algorithm: " + algorithm);

return this.getInstance(algorithm);

};

keyGenerator.getInstance.overload('java.lang.String', 'java.lang.String').implementation = function(algorithm, provider) {

console.log("[🔑] KeyGenerator.getInstance() called");

console.log(" Algorithm: " + algorithm);

console.log(" Provider: " + provider);

return this.getInstance(algorithm, provider);

};

// Hook SecretKeySpec - this is where we see actual key material

var secretKeySpec = Java.use("javax.crypto.spec.SecretKeySpec");

secretKeySpec.$init.overload('[B', 'java.lang.String').implementation = function(keyBytes, algorithm) {

var key = Java.array('byte', keyBytes);

console.log("[🗝️ ] SecretKeySpec created:");

console.log(" Algorithm: " + algorithm);

console.log(" Key (hex): " + bin2hex(key));

console.log(" Key (ascii): " + bin2ascii(key));

console.log(" Key length: " + key.length + " bytes");

return secretKeySpec.$init.overload('[B', 'java.lang.String').call(this, keyBytes, algorithm);

}

// Hook Cipher operations

var cipher = Java.use("javax.crypto.Cipher");

cipher.getInstance.overload('java.lang.String').implementation = function(transformation) {

console.log("[🔐] Cipher.getInstance() called");

console.log(" Transformation: " + transformation);

return this.getInstance(transformation);

};

cipher.init.overload('int', 'java.security.Key').implementation = function(opmode, key) {

var mode = opmode == 1 ? "ENCRYPT" : opmode == 2 ? "DECRYPT" : "UNKNOWN(" + opmode + ")";

console.log("[🔐] Cipher.init() called");

console.log(" Mode: " + mode);

console.log(" Algorithm: " + this.getAlgorithm());

return this.init(opmode, key);

};

cipher.init.overload('int', 'java.security.Key', 'java.security.spec.AlgorithmParameterSpec').implementation = function(opmode, key, params) {

var mode = opmode == 1 ? "ENCRYPT" : opmode == 2 ? "DECRYPT" : "UNKNOWN(" + opmode + ")";

console.log("[🔐] Cipher.init() called (with params)");

console.log(" Mode: " + mode);

console.log(" Algorithm: " + this.getAlgorithm());

console.log(" Params: " + params);

return this.init(opmode, key, params);

};

cipher.doFinal.overload('[B').implementation = function(input) {

console.log("[🔐] Cipher.doFinal() called");

console.log(" Input length: " + input.length + " bytes");

console.log(" Input (hex): " + bin2hex(Java.array('byte', input)));

var result = cipher.doFinal.overload("[B").call(this, input);

console.log(" Output length: " + result.length + " bytes");

console.log(" Output (hex): " + bin2hex(Java.array('byte', result)));

return result;

};

// Hook MessageDigest (hashing)

var messageDigest = Java.use("java.security.MessageDigest");

messageDigest.getInstance.overload('java.lang.String').implementation = function(algorithm) {

console.log("[🔒] MessageDigest.getInstance() called");

console.log(" Algorithm: " + algorithm);

return this.getInstance(algorithm);

};

messageDigest.digest.overload().implementation = function() {

console.log("[🔒] MessageDigest.digest() called");

console.log(" Algorithm: " + this.getAlgorithm());

var result = messageDigest.digest.overload().call(this);

var hash = Java.array('byte', result);

console.log(" Hash (hex): " + bin2hex(hash));

console.log(" Hash length: " + hash.length + " bytes");

return result;

};

messageDigest.digest.overload('[B').implementation = function(input) {

console.log("[🔒] MessageDigest.digest() called with input");

console.log(" Algorithm: " + this.getAlgorithm());

console.log(" Input length: " + input.length + " bytes");

console.log(" Input (hex): " + bin2hex(Java.array('byte', input)));

var result = messageDigest.digest.overload('[B').call(this, input);

var hash = Java.array('byte', result);

console.log(" Hash (hex): " + bin2hex(hash));

return result;

};

// Hook Mac (HMAC operations)

var mac = Java.use("javax.crypto.Mac");

mac.getInstance.overload('java.lang.String').implementation = function(algorithm) {

console.log("[🔐] Mac.getInstance() called");

console.log(" Algorithm: " + algorithm);

return this.getInstance(algorithm);

};

mac.init.overload('java.security.Key').implementation = function(key) {

console.log("[🔐] Mac.init() called");

console.log(" Algorithm: " + this.getAlgorithm());

return this.init(key);

};

mac.doFinal.overload().implementation = function() {

console.log("[🔐] Mac.doFinal() called");

console.log(" Algorithm: " + this.getAlgorithm());

var result = mac.doFinal.overload().call(this);

var hmac = Java.array('byte', result);

console.log(" HMAC (hex): " + bin2hex(hmac));

console.log(" HMAC length: " + hmac.length + " bytes");

return result;

};

// Hook Android Keystore operations

var keyStore = Java.use("java.security.KeyStore");

keyStore.getInstance.overload('java.lang.String').implementation = function(type) {

console.log("[🏪] KeyStore.getInstance() called");

console.log(" Type: " + type);

return this.getInstance(type);

};

keyStore.load.overload('java.io.InputStream', '[C').implementation = function(stream, password) {

console.log("[🏪] KeyStore.load() called");

if (password) {

console.log(" Password length: " + password.length + " chars");

}

return this.load(stream, password);

};

// Hook KeyGenParameterSpec for hardware-backed keys

try {

var keyGenBuilder = Java.use("android.security.keystore.KeyGenParameterSpec$Builder");

keyGenBuilder.$init.overload("java.lang.String", "int").implementation = function(keystoreAlias, purposes) {

var purposeStr = "";

if (purposes & 1) purposeStr += "ENCRYPT ";

if (purposes & 2) purposeStr += "DECRYPT ";

if (purposes & 4) purposeStr += "SIGN ";

if (purposes & 8) purposeStr += "VERIFY ";

console.log("[🔐] KeyGenParameterSpec.Builder created");

console.log(" Keystore alias: " + keystoreAlias);

console.log(" Purposes: " + purposeStr + "(" + purposes + ")");

return keyGenBuilder.$init.overload("java.lang.String", "int").call(this, keystoreAlias, purposes);

};

keyGenBuilder.setKeySize.implementation = function(keySize) {

console.log("[🔐] KeyGenParameterSpec: Key size set to " + keySize + " bits");

return this.setKeySize(keySize);

};

keyGenBuilder.setBlockModes.implementation = function(blockModes) {

console.log("[🔐] KeyGenParameterSpec: Block modes: " + blockModes);

return this.setBlockModes(blockModes);

};

keyGenBuilder.setEncryptionPaddings.implementation = function(paddings) {

console.log("[🔐] KeyGenParameterSpec: Encryption paddings: " + paddings);

return this.setEncryptionPaddings(paddings);

};

} catch(e) {

console.log("[!] KeyGenParameterSpec hooking failed (Android version might not support it)");

}

// Hook IvParameterSpec to catch initialization vectors

var ivSpec = Java.use("javax.crypto.spec.IvParameterSpec");

ivSpec.$init.overload("[B").implementation = function(iv) {

var ivArray = Java.array('byte', iv);

console.log("[🔒] IvParameterSpec created");

console.log(" IV (hex): " + bin2hex(ivArray));

console.log(" IV (ascii): " + bin2ascii(ivArray));

console.log(" IV length: " + ivArray.length + " bytes");

return ivSpec.$init.overload("[B").call(this, iv);

};

// Hook Signature operations

var signature = Java.use("java.security.Signature");

signature.getInstance.overload('java.lang.String').implementation = function(algorithm) {

console.log("[✍️] Signature.getInstance() called");

console.log(" Algorithm: " + algorithm);

return this.getInstance(algorithm);

};

signature.initSign.overload('java.security.PrivateKey').implementation = function(privateKey) {

console.log("[✍️] Signature.initSign() called");

console.log(" Algorithm: " + this.getAlgorithm());

return this.initSign(privateKey);

};

signature.initVerify.overload('java.security.PublicKey').implementation = function(publicKey) {

console.log("[✍️] Signature.initVerify() called");

console.log(" Algorithm: " + this.getAlgorithm());

return this.initVerify(publicKey);

};

signature.sign.overload().implementation = function() {

console.log("[✍️] Signature.sign() called");

console.log(" Algorithm: " + this.getAlgorithm());

var result = signature.sign.overload().call(this);

var sig = Java.array('byte', result);

console.log(" Signature (hex): " + bin2hex(sig));

console.log(" Signature length: " + sig.length + " bytes");

return result;

};

console.log("[+] All crypto hooks installed successfully!");

console.log("[+] Waiting for crypto operations...");

});

}, 0);

Running the Tracer

Now that you have the script, here’s how to use it:

Basic Usage

# Attach to a running app

frida -U -l crypto_tracer.js com.example.app

# Or spawn a new instance of the app

frida -U -f com.example.app -l crypto_tracer.js --no-pause

Advanced Usage with Output Logging

If you want to save everything to a file:

1 2	frida -U -l crypto_tracer.js com.example.app \| tee crypto_trace.log

Or if you want to filter only specific operations:

1 2	frida -U -l crypto_tracer.js com.example.app \| grep -E "\[🔑\]\|\[🔐\]"

Understanding the Output

When you run the tracer, you’ll see output like this:

[+] Crypto tracer started - hooking into crypto operations...

[🔑] KeyGenerator.getInstance() called

Algorithm: AES

[🔑] KeyGenerator.generateKey() called

Algorithm: AES

Key generated successfully

[🗝️ ] SecretKeySpec created:

Algorithm: AES

Key (hex): 48656c6c6f576f726c6448656c6c6f

Key (ascii): HelloWorldHello

Key length: 16 bytes

[🔐] Cipher.getInstance() called

Transformation: AES/CBC/PKCS5Padding

[🔒] IvParameterSpec created

IV (hex): 0102030405060708090a0b0c0d0e0f10

IV (ascii): ................

IV length: 16 bytes

[🔐] Cipher.init() called (with params)

Mode: ENCRYPT

Algorithm: AES/CBC/PKCS5Padding

Params: javax.crypto.spec.IvParameterSpec@a1b2c3d4

[🔐] Cipher.doFinal() called

Input length: 32 bytes

Input (hex): 54686973206973206120736563726574206d6573736167652074686174206e6565647320656e6372797074696f6e

Output length: 48 bytes

Output (hex): 3f8a9c2b1e4d6f7a8b3c9e1f2a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d9e0f1a2b

What Each Symbol Means

🔑 KeyGenerator operations – When the app generates new encryption keys
🗝️ SecretKeySpec – Shows you the actual key material being used
🔐 Cipher operations – Encryption/decryption activities with full details
🔒 MessageDigest/IV – Hashing operations and initialization vectors
✍️ Signature operations – Digital signing and verification
🏪 KeyStore operations – When the app uses Android’s secure key storage

Real-World Analysis Examples

Example 1: Banking App Analysis

Let’s say you’re analyzing a banking app. You might see:

1 2	frida -U -l crypto_tracer.js com.bank.app

Look for patterns like:

Are they using AES with proper key lengths (256-bit)?
Do they use random IVs for each encryption?
Are passwords being hashed with salt?
Are they using hardware-backed keys for sensitive operations?

Example 2: Messaging App Research

For a messaging app, you’d want to check:

1 2	frida -U -f com.chat.app -l crypto_tracer.js --no-pause

Key things to look for:

End-to-end encryption implementation
Key exchange mechanisms
Message signing for authenticity

Example 3: Custom Analysis Script

You can also create a custom analysis script that builds on our tracer:

// analysis.js - Custom script for specific app analysis
Java.perform(function() {
    // Load the base tracer first
    // Then add custom logic
    
    var suspicious_keys = [];
    var crypto_operations = [];
    
    // Override our SecretKeySpec hook to collect keys
    var originalSecretKeySpec = secretKeySpec.$init.overload('[B', 'java.lang.String').implementation;
    secretKeySpec.$init.overload('[B', 'java.lang.String').implementation = function(keyBytes, algorithm) {
        var key = Java.array('byte', keyBytes);
        var keyHex = bin2hex(key);
        
        // Check for weak keys (all zeros, repeated patterns, etc.)
        if (keyHex.match(/^(00)+$/)) {
            console.log("[⚠️ ] WARNING: All-zero key detected!");
            suspicious_keys.push({type: "zero_key", key: keyHex, algorithm: algorithm});
        }
        
        if (keyHex.match(/^(.{2})\1+$/)) {
            console.log("[⚠️ ] WARNING: Repeating pattern in key detected!");
            suspicious_keys.push({type: "pattern_key", key: keyHex, algorithm: algorithm});
        }
        
        crypto_operations.push({
            type: "key_creation",
            algorithm: algorithm,
            key: keyHex,
            timestamp: new Date().toISOString()
        });
        
        return originalSecretKeySpec.call(this, keyBytes, algorithm);
    };
    
    // Export findings after 30 seconds
    setTimeout(function() {
        console.log("\n=== ANALYSIS SUMMARY ===");
        console.log("Total crypto operations: " + crypto_operations.length);
        console.log("Suspicious keys found: " + suspicious_keys.length);
        
        if (suspicious_keys.length &gt; 0) {
            console.log("\nSUSPICIOUS KEYS:");
            suspicious_keys.forEach(function(key, index) {
                console.log((index + 1) + ". " + key.type + " - " + key.algorithm + " - " + key.key);
            });
        }
        
        // You could also export this data to a file or send it to a server
    }, 30000);
});

// analysis.js - Custom script for specific app analysis

Java.perform(function() {

// Load the base tracer first

// Then add custom logic

var suspicious_keys = [];

var crypto_operations = [];

// Override our SecretKeySpec hook to collect keys

var originalSecretKeySpec = secretKeySpec.$init.overload('[B', 'java.lang.String').implementation;

secretKeySpec.$init.overload('[B', 'java.lang.String').implementation = function(keyBytes, algorithm) {

var key = Java.array('byte', keyBytes);

var keyHex = bin2hex(key);

// Check for weak keys (all zeros, repeated patterns, etc.)

if (keyHex.match(/^(00)+$/)) {

console.log("[⚠️ ] WARNING: All-zero key detected!");

suspicious_keys.push({type: "zero_key", key: keyHex, algorithm: algorithm});

}

if (keyHex.match(/^(.{2})\1+$/)) {

console.log("[⚠️ ] WARNING: Repeating pattern in key detected!");

suspicious_keys.push({type: "pattern_key", key: keyHex, algorithm: algorithm});

}

crypto_operations.push({

type: "key_creation",

algorithm: algorithm,

key: keyHex,

timestamp: new Date().toISOString()

});

return originalSecretKeySpec.call(this, keyBytes, algorithm);

};

// Export findings after 30 seconds

setTimeout(function() {

console.log("\n=== ANALYSIS SUMMARY ===");

console.log("Total crypto operations: " + crypto_operations.length);

console.log("Suspicious keys found: " + suspicious_keys.length);

if (suspicious_keys.length > 0) {

console.log("\nSUSPICIOUS KEYS:");

suspicious_keys.forEach(function(key, index) {

console.log((index + 1) + ". " + key.type + " - " + key.algorithm + " - " + key.key);

});

}

// You could also export this data to a file or send it to a server

}, 30000);

});

Advanced Techniques

Bypassing Anti-Frida Measures

Some apps try to detect Frida. Here’s how to deal with that:

# Rename frida-server to something innocent

adb shell "mv /data/local/tmp/frida-server /data/local/tmp/system_daemon"

adb shell "/data/local/tmp/system_daemon &"

# Use a different port

adb shell "/data/local/tmp/frida-server -l 0.0.0.0:8888 &"

frida -H 127.0.0.1:8888 -l crypto_tracer.js com.example.app

Automated Analysis with Python

You can also automate the analysis with Python:

import frida

import sys

import json

import time

def on_message(message, data):

if message['type'] == 'send':

payload = message['payload']

if 'SecretKeySpec' in payload:

print(f"[KEY DETECTED] {payload}")

elif 'Cipher.doFinal' in payload:

print(f"[CRYPTO OP] {payload}")

device = frida.get_usb_device()

session = device.attach("com.example.app")

with open("crypto_tracer.js", "r") as f:

script_content = f.read()

script = session.create_script(script_content)

script.on('message', on_message)

script.load()

print("[*] Script loaded, press Ctrl+C to exit")

try:

sys.stdin.read()

except KeyboardInterrupt:

print("\n[*] Stopping...")

session.detach()

Extracting and Saving Key Material

Want to save all the key material for later analysis? Modify the script:

// Add this to the SecretKeySpec hook

var fs = Java.use("java.io.FileOutputStream");

var keyFile = "/sdcard/Download/extracted_keys.txt";

var keyData = algorithm + "|" + bin2hex(key) + "|" + new Date().toISOString() + "\n";

try {

var fos = fs.$new(keyFile, true); // true for append mode

var bytes = Java.array('byte', keyData.split('').map(c => c.charCodeAt(0)));

fos.write(bytes);

fos.close();

console.log(" Key saved to: " + keyFile);

} catch(e) {

console.log(" Failed to save key: " + e);

}

Interpreting Common Patterns

Good Crypto Practices

When you see these patterns, it usually means the app is doing things right:

[🔑] KeyGenerator.getInstance() called

Algorithm: AES

[🗝️ ] SecretKeySpec created:

Algorithm: AES

Key length: 32 bytes # 256-bit key - good!

[🔒] IvParameterSpec created

IV length: 16 bytes # Proper IV size for AES

IV (hex): a1b2c3d4e5f6... # Random-looking IV - good!

Red Flags

Watch out for these warning signs:

[🗝️ ] SecretKeySpec created:

Algorithm: DES # DES is broken!

Key (hex): 0000000000000000 # All-zero key!

Key (ascii): HelloWorld # Hardcoded key!

[🔒] MessageDigest.getInstance() called

Algorithm: MD5 # MD5 is broken for crypto!

[🔒] IvParameterSpec created

IV (hex): 0102030405060708090a0b0c0d0e0f10 # Static IV - bad!

Building Your Own Crypto Arsenal

Monitoring Specific Algorithms

If you want to focus on specific algorithms, create a targeted script:

// Focus only on AES operations

Java.perform(function() {

// ... (previous code)

var originalCipherGetInstance = cipher.getInstance.overload('java.lang.String').implementation;

cipher.getInstance.overload('java.lang.String').implementation = function(transformation) {

if (transformation.toLowerCase().includes('aes')) {

console.log("[🎯] AES operation detected: " + transformation);

// You could trigger additional analysis here

// Maybe dump the stack trace to see where it's called from

console.log("Stack trace: " + Log.getStackTraceString(Exception.$new()));

}

return originalCipherGetInstance.call(this, transformation);

};

});

Real-Time Key Analysis

Want to analyze keys as they’re created?

// Add to SecretKeySpec hook
var keyHex = bin2hex(key);
var keyStrength = analyzeKeyStrength(keyHex);

// Add to SecretKeySpec hook

var keyHex = bin2hex(key);

var keyStrength = analyzeKeyStrength(keyHex);

function analyzeKeyStrength(hexKey) {

var analysis = {

length: hexKey.length / 2,

entropy: calculateEntropy(hexKey),

patterns: findPatterns(hexKey),

strength: "unknown"

};

if (analysis.entropy < 3.0) {

analysis.strength = "weak";

console.log(" [⚠️ ] LOW ENTROPY KEY DETECTED!");

} else if (analysis.entropy > 7.0) {

analysis.strength = "strong";

console.log(" [✅] Good entropy detected");

}

return analysis;

}

function calculateEntropy(hexString) {

var frequency = {};

var entropy = 0;

for (var i = 0; i < hexString.length; i++) {

var char = hexString[i];

frequency[char] = (frequency[char] || 0) + 1;

}

for (var char in frequency) {

var p = frequency[char] / hexString.length;

entropy -= p * Math.log2(p);

}

return entropy;

}

Troubleshooting Common Issues

App Crashes When Hooking

If the app crashes, try:

Hook selectively: Start with just one or two hooks to identify the problematic one
Check Android version: Some crypto APIs changed between Android versions
Use try-catch blocks: Wrap hooks in try-catch to prevent crashes

try {

cipher.doFinal.overload('[B').implementation = function(input) {

// Your hook code here

};

} catch(e) {

console.log("[!] Failed to hook Cipher.doFinal: " + e);

}

Missing Crypto Operations

If you’re not seeing expected crypto operations:

Check native libraries: The app might be using native crypto
Look for obfuscation: Class names might be obfuscated
Hook earlier: Some operations happen during app initialization

Performance Issues

If the app becomes slow:

Reduce logging: Only log what you really need
Use conditional hooks: Only hook when certain conditions are met
Buffer output: Collect data and output in batches

Taking It Further

Integration with Other Tools

Combine Frida tracing with:

Static analysis: Compare with what tools like JADX show you
Network monitoring: Use Burp Suite or mitmproxy alongside
Binary analysis: Check native libraries with tools like Ghidra

Building a Crypto Testing Framework

You could build a complete framework:

# crypto_analyzer.py

class CryptoAnalyzer:

def __init__(self, package_name):

self.package = package_name

self.findings = []

self.device = frida.get_usb_device()

def analyze_keys(self):

# Load key analysis script

pass

def analyze_algorithms(self):

# Load algorithm analysis script

pass

def generate_report(self):

# Generate comprehensive report

pass

# Usage

analyzer = CryptoAnalyzer("com.example.app")

analyzer.analyze_keys()

analyzer.analyze_algorithms()

report = analyzer.generate_report()

Continuous Monitoring

Set up continuous monitoring for apps in development:

#!/bin/bash

# crypto_monitor.sh

APP_PACKAGE="com.yourapp.debug"

LOG_DIR="/tmp/crypto_logs"

DATE=$(date +%Y%m%d_%H%M%S)

mkdir -p $LOG_DIR

echo "Starting crypto monitoring for $APP_PACKAGE"

frida -U -l crypto_tracer.js $APP_PACKAGE > "$LOG_DIR/crypto_trace_$DATE.log" 2>&1 &

FRIDA_PID=$!

echo "Frida PID: $FRIDA_PID"

# Monitor for 10 minutes

sleep 600

kill $FRIDA_PID

echo "Monitoring complete. Log saved to $LOG_DIR/crypto_trace_$DATE.log"

# Analyze the log

python analyze_crypto_log.py "$LOG_DIR/crypto_trace_$DATE.log"

Wrapping Up

At this point, you should have a solid understanding of how to trace crypto operations in Android apps. This technique gives you incredible visibility into what’s really happening with sensitive data.

Remember, with great power comes great responsibility. Use these techniques ethically and only on apps you have permission to analyze. Whether you’re doing security research, debugging your own code, or just satisfying your curiosity, always respect privacy and follow responsible disclosure practices.

The crypto landscape is constantly evolving, and so should your analysis techniques. Keep experimenting, keep learning, and most importantly, keep making the mobile world a more secure place.

Now go forth and uncover those crypto secrets! And remember – if you find something interesting, the community always appreciates researchers who share their knowledge responsibly.

Catching Crypto Secrets in Android Apps with Frida

Why This Matters

Setting Up Your Lab

The Basics

Finding Your Target

Understanding the Crypto Landscape

The Complete Tracing Script

Running the Tracer

Basic Usage

Advanced Usage with Output Logging

Understanding the Output

What Each Symbol Means

Real-World Analysis Examples

Example 1: Banking App Analysis

Example 2: Messaging App Research

Example 3: Custom Analysis Script

Advanced Techniques

Bypassing Anti-Frida Measures

Automated Analysis with Python

Extracting and Saving Key Material

Interpreting Common Patterns

Good Crypto Practices

Red Flags

Building Your Own Crypto Arsenal

Monitoring Specific Algorithms

Real-Time Key Analysis

Troubleshooting Common Issues

App Crashes When Hooking

Missing Crypto Operations

Performance Issues

Taking It Further

Integration with Other Tools

Building a Crypto Testing Framework

Continuous Monitoring

Wrapping Up

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