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Previously, Arduino Core attempted to read from flash memory without proper consideration for the 4-byte alignment requirement when calculating the hash for the signature verification. This did not present an issue when uncompressed binaries are checked as all compiled binaries are 4-aligned (unconfirmed, just an educated guess), and signature verification appears to work well in these cases. When uploading a compressed binary (based on this) the gzip algorithm makes no attempt to produce a 4-aligned file. The rest of the signing results in a valid signed binary regardless, however when calculating the hash for the verification process there is a ~75% chance that the hash will include some bytes from the signature, thus compromising the whole signature verification process. editorial note: ESP.flashRead for u8 arrays (aka byte arrays) was already updated to properly handle both aligned and unaligned target buffer and / or length, while u32 expects that its arguments are already aligned. Since array pointer in Updater is already aligned, this properly handles unaligned size case.