A New Method for Format Preserving Encryption in High-Data Rate Communications

Abstract

In some encryption systems it is necessary to preserve the format and length of the encrypted data. This kind of encryption is called FPE (Format Preserving Encryption). Currently, only two AES (Advanced Encryption Standard) modes of operation recommended by the NIST (National Institute of Standards and Technology) are able to implement FPE algorithms, FF1 and FF3. These modes work in an electronic codebook fashion and can be configured to encrypt databases with an arbitrary format and length. However, there are no stream cipher proposals able to implement FPE encryption for high data rate information flows. The main novelty of this work is a new block cipher operation mode proposal to implement an FPE algorithm in a stream cipher fashion. It has been called CTR-MOD and it is based on a standard block cipher working in CTR (Counter) mode and a modulo operation. The confidentiality of this mode is analyzed in terms of its IND-CPA (Indistinguishability under Chosen Plaintext Attack) advantage of any adversary attacking it. Moreover, the encryption scheme has been implemented on an FPGA (Field Programmable Gate Array) and has been integrated in a Gigabit Ethernet interface to test an encrypted optical link with a real high data rate traffic flow. INDEX TERMS FPE (format preserving encryption), stream cipher, FPGA (field programmable gate array), Ethernet.

Self-Synchronized Encryption for Physical Layer in Gigabit Ethernet Optical Links

“…7 has been synthetized in a Xilinx Virtex 7 FPGA (Field Programmable Gate Array) and the hardware resources used by this solution are shown in Table 2 in terms of LUTs (Look-Up Tables), registers and block RAMs. In this table PSCFB-MOD implementation is compared with other FPE implementations [33], [20], showing that this work entails a good Encryption_Rate/resource ratio. Although in this work the mode PSCFB-MOD entails more hardware resources than CTR-MOD [20], it is at expense of adding the self-synchronization property.…”

“…We assume that in both modes it is used a secure underlying block cipher E K that can be considered a good PRP, which means that the term ADV PRP E K is negligible in both expressions, (17) and (18). According to this, it is only necessary to compare the second term of both advantage expressions to meet (19), as shown in (20).…”

“…where T = log 2 S ∼ = 8.06 and I = L − T . In this work, we have used the same structure for F K _MOD than in [20], letting parameters l and L as fixed values such that l = 192 and L = 149. Therefore to accomplish with (25) it is also necessary that L IV ≥ 17.…”

“…In the same way as in [20], to get a block size l = 192, we have used as underlying block cipher E K a Rijndael structure configured with 192 bit block size and 128 bit key length. For modulo operation functions, the block MOD_2 149 of Fig.…”

“…In order to reduce the hardware complexity of possible selfsynchronous FPE stream ciphers, in this work a new structure able to preserve the format of the plaintext is proposed. It is based on a recommended block cipher working in an operation mode that is a synergic combination of PSCFB and CTR-MOD [20] modes. We have called it PSCFB-MOD.…”