Not All Is Lost: Partial Recovery & Memorability in Self-Sovereign Digital Identity

The shift toward Self-Sovereign Digital Identity (SSDI) promises to mitigate the epidemic of massive personal data leaks, but it fundamentally relies on users securely managing high-strength private keys. Traditional backup methods, such as hardware wallets, paper records, and cloud vaults, inevitably compromise either security, locality, or availability. While human memory offers a uniquely theft-proof and local alternative, the cognitive burden of memorizing strong cryptographic keys remains a critical usability barrier. Crucially, prior usable security research has largely treated key memorability as a binary outcome — either perfectly recalled or completely forgotten. We challenge this paradigm through a lab-based randomized controlled trial (N=92) of 128-bit (NIST-minimum) keys. Comparing standard 12-word BIP-39 mnemonics against a graphical key scheme, we demonstrate how combinatorial search can leverage fragmented human memory to reconstruct keys without degrading theoretical security bounds. We present an empirical evaluation of how cognitive-science principles affect memorability of full 128-bit system-assigned keys, paired with a novel computational recovery technique. Our findings reveal an advantage for graphical keys, suggesting that augmenting BIP-39 mnemonics with graphical cues and combinatorial recovery of partially forgotten keys may offer a promising path forward.