A method of transmitting a first digital content file from a first sender device configured with a key library to a receiver device configured with a receiver identity and a first sender-receiver key is disclosed. The method includes identifying the first sender-receiver key within the key library based on the receiver identity. The method also includes encrypting a first digital message, the first digital message including the first digital content file and a code to derive a second sender-receiver key, with the first sender-receiver key. The method further includes transmitting the first digital message to the receiver device; decrypting the first digital message with the first sender-receiver key; deriving the second sender-receiver key based on the code; and replacing the first sender-receiver key with the second sender-receiver key.