This would help if you _only_ shared the prefix, however git would still use the full hash. The proposed method would have the advantage of keeping existing kn

This would help if you _only_ shared the prefix, however git would still use the full hash. The proposed method would have the advantage of keeping existing known abbreviations, which are _already_ less secure than SHA-1, while keeping the security of the second hash. It also has the disadvantage that the full hash would become excessively large and unwieldy, so pros and cons.