[Back] Enter a message, and generate a code:

abcdefghijklmnopqrstuvwxyz

QVZACHRUBDWJOPTXGFESLNYKIM

The previous unit outlined how data can be encrypted so that it cannot be viewed by anyone that it was not intended from. With private-key encryption, Bob and Alice use the same secret key to encrypt and decrypt the message. Then, using a key interchange method such as Diffie-Hellman, Bob and Alice can generate the same secret key, even if Eve is listening to their communications. With public-key encryption, Bob and Alice do not have the same problem, as Alice can advertise her public key so that Bob can use it to encrypt communications to her. The only key that can decrypt the communications is Alice’s private key (which, hopefully, Eve cannot get hold off). We now, though, have four further problems:- How do we know that it was really Bob who sent the data, as anyone can get Alice’s public key, and thus pretend to be Bob? - How can we tell that the message has not been tampered with? - How does Bob distribute his public key to Alice, without having to post it onto a Web site or for Bob to be on-line when Alice reads the message? - Who can we really trust to properly authenticate Bob? Obviously we can’t trust Bob to authenticate that he really is Bob. These questions will be answered in this unit, as we will look at the usage of hashing to finger-print data, and then how Bob’s private key can be used to authenticate himself. Finally, it will look at the way that a public key can be distributed, using digital certificates, which can carry encryption key. This chapter will show the importance of authentication and assurance, along with confidentiality (Figure 4.1), and the usage of biometrics.

SUC XFCNBTLE LPBS TLSJBPCA UTY AQSQ ZQP VC CPZFIXSCA ET SUQS BS ZQPPTS VC NBCYCA VI QPITPC SUQS BS YQE PTS BPSCPACA HFTO. YBSU XFBNQSC-WCI CPZFIXSBTP, VTV QPA QJBZC LEC SUC EQOC ECZFCS WCI ST CPZFIXS QPA ACZFIXS SUC OCEEQRC. SUCP, LEBPR Q WCI BPSCFZUQPRC OCSUTA ELZU QE ABHHBC-UCJJOQP, VTV QPA QJBZC ZQP RCPCFQSC SUC EQOC ECZFCS WCI, CNCP BH CNC BE JBESCPBPR ST SUCBF ZTOOLPBZQSBTPE. YBSU XLVJBZ-WCI CPZFIXSBTP, VTV QPA QJBZC AT PTS UQNC SUC EQOC XFTVJCO, QE QJBZC ZQP QANCFSBEC UCF XLVJBZ WCI ET SUQS VTV ZQP LEC BS ST CPZFIXS ZTOOLPBZQSBTPE ST UCF. SUC TPJI WCI SUQS ZQP ACZFIXS SUC ZTOOLPBZQSBTPE BE QJBZC’E XFBNQSC WCI (YUBZU, UTXCHLJJI, CNC ZQPPTS RCS UTJA THH). YC PTY, SUTLRU, UQNC HTLF HLFSUCF XFTVJCOE:- UTY AT YC WPTY SUQS BS YQE FCQJJI VTV YUT ECPS SUC AQSQ, QE QPITPC ZQP RCS QJBZC’E XLVJBZ WCI, QPA SULE XFCSCPA ST VC VTV? - UTY ZQP YC SCJJ SUQS SUC OCEEQRC UQE PTS VCCP SQOXCFCA YBSU? - UTY ATCE VTV ABESFBVLSC UBE XLVJBZ WCI ST QJBZC, YBSUTLS UQNBPR ST XTES BS TPST Q YCV EBSC TF HTF VTV ST VC TP-JBPC YUCP QJBZC FCQAE SUC OCEEQRC? - YUT ZQP YC FCQJJI SFLES ST XFTXCFJI QLSUCPSBZQSC VTV? TVNBTLEJI YC ZQP’S SFLES VTV ST QLSUCPSBZQSC SUQS UC FCQJJI BE VTV. SUCEC GLCESBTPE YBJJ VC QPEYCFCA BP SUBE LPBS, QE YC YBJJ JTTW QS SUC LEQRC TH UQEUBPR ST HBPRCF-XFBPS AQSQ, QPA SUCP UTY VTV’E XFBNQSC WCI ZQP VC LECA ST QLSUCPSBZQSC UBOECJH. HBPQJJI, BS YBJJ JTTW QS SUC YQI SUQS Q XLVJBZ WCI ZQP VC ABESFBVLSCA, LEBPR ABRBSQJ ZCFSBHBZQSCE, YUBZU ZQP ZQFFI CPZFIXSBTP WCI. SUBE ZUQXSCF YBJJ EUTY SUC BOXTFSQPZC TH QLSUCPSBZQSBTP QPA QEELFQPZC, QJTPR YBSU ZTPHBACPSBQJBSI (HBRLFC 4.1), QPA SUC LEQRC TH VBTOCSFBZE.

This table shows the occurances of the letters in the text (ignoring the case of the letters):

This table shows how the text matches a normal probability to text (where 'E' has the highest level of occurance and 'Z' has the least). The grey rows show what would be expected for the order, and the red one shows what your text gives for the order: