CSE 190 -- Lecture 6-7 -- Apr 10, 13

ECB and CBC modes. Block vs stream ciphers. How to model them mathematically. Why Big-O is typically inappropriate, since brute-force decryption is O(1).

There's been some complaints that letter frequencies were not made available. Being CS-types, I expected you to be able to write the short C, C++, Java, perl, or whatever language programs to calculate this over your own sample text, e.g., email, web pages, etc. Included below is a perl program to compute letter frequencies; if you think you need digram frequencies, you can write it / extend it yourself, though you should be able to, by using common sense / observations of actual English text, guess what the more frequent letter pairs that you'd encounter.

perl -e '
while (<>) {
	@chars=split / */,$_;
	for $letter (@chars) {
for $letter (keys %freq) {
	print "$letter: ",$freq{$letter},"\n";
} '

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