| CPC H04L 9/0863 (2013.01) [G06F 21/45 (2013.01); H04L 9/008 (2013.01)] | 20 Claims |

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1. A system, comprising:
a password management system implemented by a one or more computer systems, configured to:
perform a password conformity check on a first password, including to:
perform a homomorphic encryption operation on the first password to obtain a first character string, wherein the homomorphic encryption operation when performed on two given strings produces two encrypted strings that preserve a distance between the two given strings;
compare the first character string to a previous character string stored in a password data store and generated by the homomorphic encryption operation on a previous password to determine a first password similarity value between the first password and the previous password; and
based on the first password similarity value, reject the first password and request an alternative password;
perform the password conformity check on the alterative password, including to:
perform the homomorphic encryption operation on the alternative password to generate a second character string;
compare the second character string to the previous character string to determine a second password similarity value;
accept the alternative password based on the second password similarity value; and
store the second character string generated from the alternative password in the password data store.
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