Method and system for standard-compliant, confidential receipt of data for encrypted data processing

A computer-implemented method for standard-compliant, confidential receipt of data, wherein the method is executable via a system for data processing, in particular a system for standard-compliant, confidential receipt of data, the system comprising:

• at least one client, wherein the client is set up to send data,
• at least one server, wherein the server has implemented a cryptographic protocol for encrypting data and is set up to receive data from the client,
• at least one proxy server located on a communication path between the client and the server, wherein communication between the client and the server runs partially or completely via the proxy server,
• the method comprising the following steps:
• A. exchanging data for calculating a shared key k between the client and the server, wherein the server derives at least one key kEnc from the key k, wherein kEnc is identical to k or is calculated from k, using a key derivation function or a hash function,
• B. sending data from the client to the server, wherein the data is encrypted using an operating mode in which block ciphers are operated for a symmetric encryption application, wherein the i-th message ti from the client to the server contains an encryption Mi⊕Ki, wherein Mi is the plain-text data of the i-th message and Ki is the key of the operating mode, which is derived from kEnc and the value ti is the cryptographic value of the message,
• C. receiving the data by the proxy server and processing the value ti in accordance with the cryptographic protocol, wherein ti is the cryptographic value of the message,
• D. selecting a random string Ri by the proxy server, wherein the length of the random string Ri corresponds to the length of Mi⊕Ki,
• E. forwarding Mi⊕Ki⊕Ri to the server through the proxy server and storing the random string Ri by the proxy server,
• F. receiving Mi⊕Ki⊕Ri by the server and calculating the value Mi⊕Ri using the key Ki, wherein Ri⊕(Mi⊕Ri)=Mi applies, whereby the proxy server and the server each obtain an additive ⊕ secret sharing of the data Mi,
• wherein the method for sending a message
• M
• j
• ′
• comprises the following steps:
• G. calculating an encryption of a secret share
• (
• R
• j
• ′
• ⊕
• M
• j
• ′
• )
• ⊕Kj via the server, wherein Kj is derived from kEnc and
• (
• R
• j
• ′
• ⊕
• M
• j
• ′
• )
• is the secret share of
• M
• j
• ′
• held by the server,
• H. sending the encryption to the proxy server via the server, calculating a cipher text
• M
• j
• ′
• ⊕
• K
• j
• via the proxy server by applying a share
• R
• j
• ′
• .