The Secret Key encoder used 26 base-30 characters which can only
represent 30^26 ≈ 2^127.58 values. Since the key is 128 bits,
~25% of generated keys silently lost their high bits during
formatting, making the Emergency Kit key unable to reconstruct
the original bytes on a new browser.
Changed KEY_CHAR_LENGTH from 26 to 27 (30^27 > 2^128). Parser
accepts both old 26-char and new 27-char keys for backward
compatibility. Format: A3-XXXXXX-XXXXXX-XXXXXX-XXXXXX-XXX
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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