NTT Develops Secure Public-Key Encryption Scheme

["Nobuki Nakatuji" <bd1011@hotmail.com>]

http://pr.info.ntt.co.jp/news/news98e/980416.html

          Nippon Telegraph and Telephone Corporation (NTT) announced 
today the development of 
          Efficient Probabilistic Public-Key Encryption (EPOC), a highly 
secure and mathematically 
          verified public-key encryption scheme that encrypts 
information on the transmission side 
          with a public-key (encryption key) and then decrypts it on the 
receiver side with a secret
          -key (decryption key).

          Encryption technology has become necessary to prevent 
information on the Internet from 
          being monitored by others without authorization. Public-key 
encryption is being widely 
          researched as a practical means of encrypting communication 
for security.

          The paramount feature of any public-key encryption schemes is 
ensuring that figuring out 
          the decryption key from the encryption key is as difficult as 
possible, to prevent 
          unauthorized use of ciphered information. The RSA*1 scheme 
uses factoring and the elliptic 
          curve encryption scheme*2 uses elliptic curve discrete 
logarithms, both of which can take 
          a supercomputer a very long time to determine the key. It has 
not been verified, however, 
          that either scheme provides the necessary security to prevent 
ciphered information from 
          being broken by a method other than factoring or elliptic 
curve discrete logarithms. The 
          Rabin encryption scheme*3, which also uses factoring, offers 
no algorithm other than 
          factoring for computing the complete plain-text, but it has 
not been proven that any bit 
          of plain-text cannot be computed.

          EPOC is a practical scheme in that the computer computation 
workload for encrypting and 
          decrypting is about the same as that for the RSA and elliptic 
curve encryption schemes. 
          Also, EPOC is a highly secure scheme which uses a trapdoor 
discrete logarithm*4  as the 
          key mathematical technique and can be broken only by 
factoring. Factoring is difficult 
          to accomplish, even with a supercomputer, and the probability 
that an efficient solution 
          to factoring will be found soon is very low, because 
mathematicians have been studying 
          the problem for years. EPOC ensures that partial, as well as 
whole, texts cannot be broken. 
          Finally, EPOC uses probabilistic encryption, so re-encrypted 
text is encrypted differently 
          each time, unlike the Rabin and RSA scheme, which use 
deterministic encryption.
           
          NTT now plans to incorporate EPOC in systems for enhanced 
security on the Internet. 
          Public-key encryption is used primarily for key distribution, 
because computation load is 
          greater than that for secret-key encryption*5, so EPOC will be 
used in existing encryption 
          modules for key distribution.

          Other applications will also be developed. In particular, EPOC 
is suitable for electronic 
          voting and anonymous telecommunication since it has a 
homomorphic property, unlike the RSA, 
          Rabin and elliptic curve encryption schemes. The theoretical 
details will be presented at 
          Eurocrypt '98 in Finland this June. 


          Notes:  

          *1: The RSA scheme was developed by Rivest, Shamir, and 
Adleman in 1978 and is based on 
          the difficulty of factoring. It was the first public-key 
encryption scheme.

          *2: The elliptic curve encryption scheme was proposed 
independently by Miller and Koblitz 
          in 1985 and is based on the difficulty of elliptic curve 
discrete logarithms. The basic 
          technique is based on a scheme developed by Diffie and Hellman 
in 1976.

          *3: The Rabin scheme was developed by Rabin in 1979 and is 
based on the difficulty of 
          factoring. It was the first public-key encryption scheme to 
verify the impossibility of 
          breaking a complete text without factoring the public-key.
          *4: A trapdoor discrete logarithm is a newly discovered 
discrete logarithm problem that 
          can be solved only if a secret-key is known.

          *5: Secret-key encryption differs from public-key encryption 
in that the sender and the 
          receiver use the same key for encryption and decryption.





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