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CPSC 42500 Homework 9: Certificates and PKI, Applications
of Encryption
1. (3 pts) Translate the following expression for a simple digitally-signed certificate to a
formula, using the same notation and variable names used in the lecture.
“Bob’s public key pkB is concatenated with the string ‘Bob, Inc.’ and the date string ‘202004-27’. The resulting string is hashed, and the result is encrypted with the certificate
authority’s secret key skCA to produce signature s.”
C = H (pkB + ‘Bob, Inc’ + ‘2020-04-27’)
s = EskCA (C)
2. (2 pts) Explain why the use of Certificate Authorities does not eliminate the need for trust on
the web. Since it does not do this, what is it good for?
Certificate authorities provide root certificates for authentication and security of software on
the internet. The use of certificate authorities does not eliminate the...
