Pros of andOTP

• Open-source and fully free, with no proprietary components
• Supports encrypted backups and export options
• Offers advanced features like custom icons and tags for better organization

Cons of andOTP

• Less user-friendly interface compared to 2FAS
• Limited cross-platform support (Android-only)
• Fewer customization options for the app's appearance

Code Comparison

andOTP uses Kotlin for its Android implementation:

class TOTPHelper {
    fun generateTOTP(secret: String, time: Long, digits: Int, algorithm: String): String {
        val hmac = Mac.getInstance(algorithm)
        hmac.init(SecretKeySpec(Base32().decode(secret), algorithm))
        val hash = hmac.doFinal(ByteBuffer.allocate(8).putLong(time / 30000).array())
        val offset = hash[hash.size - 1].toInt() and 0xf
        val binary = ByteBuffer.wrap(hash).getInt(offset) and 0x7fffffff
        return String.format("%0${digits}d", binary % 10.pow(digits))
    }
}

2FAS Android uses Java:

public class TOTPGenerator {
    public static String generateTOTP(String secret, long time, int digits, String algorithm) {
        byte[] key = Base32.decode(secret);
        byte[] data = ByteBuffer.allocate(8).putLong(time / 30000).array();
        byte[] hash = HmacUtils.hmac(algorithm, key, data);
        int offset = hash[hash.length - 1] & 0xf;
        int binary = ByteBuffer.wrap(hash).getInt(offset) & 0x7fffffff;
        return String.format("%0" + digits + "d", binary % (int) Math.pow(10, digits));
    }
}

Both implementations follow similar logic for TOTP generation, with minor differences in language-specific syntax and method names.

Pros of Aegis

• Open-source and fully auditable, enhancing trust and security
• Supports a wider range of 2FA methods, including HOTP and Steam
• More customization options for the user interface

Cons of Aegis

• Less intuitive user interface for beginners
• Lacks built-in cloud backup and sync features
• Smaller user base, potentially leading to slower development and updates

Code Comparison

Both projects are written in Kotlin for Android development. Here's a brief comparison of their code structure:

2FAS Android:

class TotpTokenGenerator(private val secret: String) {
    fun generate(timestamp: Long): String {
        // TOTP generation logic
    }
}

Aegis:

class TOTPGenerator(private val secret: ByteArray) : OTPGenerator {
    override fun generate(counter: Long): String {
        // TOTP generation logic
    }
}

Both implementations follow similar patterns for OTP generation, with Aegis using a more generic approach through an interface.

Pros of FreeOTP

• Open-source and maintained by Red Hat, providing a high level of trust and security
• Lightweight and simple interface, focusing on core OTP functionality
• Supports both HOTP and TOTP protocols

Cons of FreeOTP

• Limited feature set compared to 2FAS
• Less frequent updates and potentially slower development cycle
• Fewer customization options for users

Code Comparison

FreeOTP:

public class Token implements Comparable<Token> {
    public static final String TOTP = "totp";
    public static final String HOTP = "hotp";
    private String issuerInt;
    private String issuerExt;
    private String label;
    private String imageUrl;
}

2FAS:

data class Service(
    @PrimaryKey val id: String = UUID.randomUUID().toString(),
    val name: String,
    val secret: String,
    val serviceTypeId: Long,
    val otpLink: String? = null,
    val otpLabel: String? = null,
    val otpAccount: String? = null,
    val otpIssuer: String? = null,
    val otpDigits: Int = 6,
    val otpPeriod: Int = 30,
    val otpAlgorithm: String = "SHA1",
    val backupSyncStatus: BackupSyncStatus = BackupSyncStatus.NOT_SYNCED,
    val updatedAt: Long = System.currentTimeMillis(),
    val badgeColor: Int? = null,
    val selectedImageType: SelectedImageType = SelectedImageType.IconCollection,
    val iconCollectionId: String? = null,
    val labelText: String? = null,
    val labelColor: Int? = null,
    val groupId: String? = null,
    val isDeleted: Boolean = false
)

The code comparison shows that 2FAS offers a more comprehensive data model for services, including additional features like backup sync status, badge colors, and grouping options, while FreeOTP focuses on essential OTP token information.

Pros of Google Authenticator

• Developed and maintained by Google, ensuring high security standards and regular updates
• Simple and straightforward user interface, making it easy for beginners to use
• Lightweight app with minimal resource usage

Cons of Google Authenticator

• Limited features compared to 2FAS, lacking advanced options like custom icons or categories
• No built-in backup or sync functionality, making it challenging to transfer accounts between devices
• Less frequent updates and slower adoption of new features

Code Comparison

Google Authenticator uses a more traditional approach to generating TOTP codes:

long time = System.currentTimeMillis() / 1000 / 30;
byte[] data = new byte[8];
for (int i = 8; i-- > 0; time >>>= 8) {
    data[i] = (byte) time;
}

2FAS implements a more modern and flexible approach:

fun generateCode(secret: String, time: Long): String {
    val hmac = Mac.getInstance("HmacSHA1")
    hmac.init(SecretKeySpec(secret.toByteArray(), "RAW"))
    val hash = hmac.doFinal(ByteBuffer.allocate(8).putLong(time / 30).array())
    val offset = hash[hash.size - 1].toInt() and 0xf
    val truncatedHash = hash.copyOfRange(offset, offset + 4)
    return (ByteBuffer.wrap(truncatedHash).int and 0x7fffffff % 1000000).toString().padStart(6, '0')
}

Both implementations achieve the same goal, but 2FAS's code is more readable and flexible, allowing for easier customization and extension.