| CPC H04L 9/088 (2013.01) | 20 Claims |

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1. A method comprising:
determining, by a first client device, a message key used to encrypt messages associated with a conversation;
generating, by the first client device, a key ciphertext corresponding to the message key by:
determining a prior secret key that is different from the message key;
determining a current secret key by hashing the prior secret key and the message key; and
generating the key ciphertext by encrypting the prior secret key and the message key using the current secret key; and
transmitting, by the first client device, the key ciphertext to a server system that is remote from the first client device, wherein a second client device is configured to receive the key ciphertext from the server system and decrypt the key ciphertext using the current secret key to derive the message key and decrypt the messages.
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