Root-cause write-ups, API reasoning and defect post-mortems from building RockyGuard, a tamper-resistant C++17 license library.https://rockyguard.dev/en-ushttps://rockyguard.dev/blog/no-branch-to-patch/https://rockyguard.dev/blog/no-branch-to-patch/A licence check is a boolean an attacker can patch. So we removed the branch: the feature decrypts its own data with a key only a valid licence carries.Sat, 12 Sep 2026 00:00:00 GMTengineering-notessecuritycryptographyhttps://rockyguard.dev/blog/the-public-key-you-cant-read-but-can-overwrite/https://rockyguard.dev/blog/the-public-key-you-cant-read-but-can-overwrite/Reading an embedded verification key is harmless — the attack is overwriting it. How we made key substitution tamper-evident and fail-closed.Sun, 30 Aug 2026 00:00:00 GMTengineering-notessecuritycryptographyhttps://rockyguard.dev/blog/the-branch-an-attacker-patches/https://rockyguard.dev/blog/the-branch-an-attacker-patches/Crypto makes a licence unforgeable, so attackers patch the branch that trusts it. How we obfuscate that branch, and why your own call site matters more.Sat, 29 Aug 2026 00:00:00 GMTengineering-notessecuritybuild-and-packaginghttps://rockyguard.dev/blog/the-file-on-disk-is-clean/https://rockyguard.dev/blog/the-file-on-disk-is-clean/The on-disk signature check hashes a file that an in-memory patch never touches, and it skips static builds entirely. A trust-on-first-use check for the gap.Sat, 29 Aug 2026 00:00:00 GMTengineering-notessecurityhttps://rockyguard.dev/blog/an-hmac-salted-with-a-filename/https://rockyguard.dev/blog/an-hmac-salted-with-a-filename/A valid licence could be denied outright, and the documented remedy never cleared it. The salt depended on how the licence was named, not on which anchor.Tue, 25 Aug 2026 00:00:00 GMTpostmortemcryptographyhttps://rockyguard.dev/blog/fifty-six-diagnostic-codes/https://rockyguard.dev/blog/fifty-six-diagnostic-codes/The library already knew why verification failed, then threw the distinction away. Promoting it to a public enum, without touching LicenseStatus.Tue, 25 Aug 2026 00:00:00 GMTengineering-notesapi-designabihttps://rockyguard.dev/blog/the-licence-has-not-expired/https://rockyguard.dev/blog/the-licence-has-not-expired/A per-section diagnostic can't answer the ticket that costs the most. What it took to correlate across a report instead, and what we refused to build.Tue, 25 Aug 2026 00:00:00 GMTengineering-notesdiagnostics