- 2.1 Representing Ordinary Strings
- 2.2 Representing Strings with Alternate Notations
- 2.3 Using Here-Documents
- 2.4 Finding the Length of a String
- 2.5 Processing a Line at a Time
- 2.6 Processing a Byte at a Time
- 2.7 Performing Specialized String Comparisons
- 2.8 Tokenizing a String
- 2.9 Formatting a String
- 2.10 Using Strings As IO Objects
- 2.11 Controlling Uppercase and Lowercase
- 2.12 Accessing and Assigning Substrings
- 2.13 Substituting in Strings
- 2.14 Searching a String
- 2.15 Converting Between Characters and ASCII Codes
- 2.16 Implicit and Explicit Conversion
- 2.17 Appending an Item Onto a String
- 2.18 Removing Trailing Newlines and Other Characters
- 2.19 Trimming Whitespace from a String
- 2.20 Repeating Strings
- 2.21 Embedding Expressions Within Strings
- 2.22 Delayed Interpolation of Strings
- 2.23 Parsing Comma-Separated Data
- 2.24 Converting Strings to Numbers (Decimal and Otherwise)
- 2.25 Encoding and Decoding rot13 Text
- 2.26 Encrypting Strings
- 2.27 Compressing Strings
- 2.28 Counting Characters in Strings
- 2.29 Reversing a String
- 2.30 Removing Duplicate Characters
- 2.31 Removing Specific Characters
- 2.32 Printing Special Characters
- 2.33 Generating Successive Strings
- 2.34 Calculating a 32-Bit CRC
- 2.35 Calculating the MD5 Hash of a String
- 2.36 Calculating the Levenshtein Distance Between Two Strings
- 2.37 Encoding and Decoding base64 Strings
- 2.38 Encoding and Decoding Strings (uuencode/uudecode)
- 2.39 Expanding and Compressing Tab Characters
- 2.40 Wrapping Lines of Text
- 2.41 Conclusion
This chapter is from the book
This chapter is from the book
This chapter is from the book
2.25 Encoding and Decoding rot13 Text
The rot13 method is perhaps the weakest form of encryption known to humankind. Its historical use is simply to prevent people from "accidentally" reading a piece of text. It is commonly seen in Usenet; for example, a joke that might be considered offensive might be encoded in rot13, or you could post the entire plot of Star Wars: Episode 12 on the day before the premiere.
The encoding method consists simply of "rotating" a string through the alphabet, so that A becomes N, B becomes O, and so on. Lowercase letters are rotated in the same way; digits, punctuation, and other characters are ignored. Because 13 is half of 26 (the size of our alphabet), the function is its own inverse; applying it a second time will "decrypt" it.
The following example is an implementation as a method added to the String class. We present it without further comment:
class String
def rot13
self.tr("A-Ma-mN-Zn-z","N-Zn-zA-Ma-m")
end
end
joke = "Y2K bug"
joke13 = joke.rot13 # "L2X oht"
episode2 = "Fcbvyre: Naanxva qbrfa'g trg xvyyrq."
puts episode2.rot13