How Can I Ensure Consistent HOTP Generation Between Java and Golang Implementations?

Contrast between Java and Golang for RFC-4226 HOTP Implementation

Generating Valid HOTP in Golang

Your initial code in Golang to generate HOTP differs from its Java counterpart, causing disparities in the resulting byte arrays. The underlying issue stems from the distinct byte representation in Java and Golang. Java's byte type is signed, with a range of -128 to 127, while in Golang, byte is an alias of uint8, with a range of 0 to 255.

To achieve consistency, it's crucial to normalize the negative Java byte values by adding 256. This adjustment aligns the byte arrays generated in Java and Golang.

Byte Encoding Differences

Another difference between your Java and Golang code is the encoding method. Java returns the hex-encoded result, while Golang returns the Base64-encoded result. To match the Java output, you need to replace the base64 encoding in Golang with hex encoding.

Signed vs. Unsigned Byte Display

For debugging purposes, you can display signed byte values in Java using the expression "byteValue & 0xff." This converts a byte value to an int, representing the byte's 8 bits as the least significant bits of the resulting int.

In Go, you can display bytes as signed values by converting them to int8. For instance, "fmt.Print(int8(b))" will print a byte as its signed equivalent.

Conclusion

Understanding the differences in byte representation and encoding between Java and Golang allows for accurate HOTP implementation in Golang. By addressing these disparities, you can generate valid HOTP codes in your Go applications.

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