4 ms·

So, a simple substitution cipher? Should be trivial to crack.

smcl 13y ago
For this guy yes, but for not necessarily everyone. The messages don't seem to be particularly long so it's unlikely a frequency based attack could work. Also if it is then these guys will not exactly be using the Queen's English so they'll likely have a different letter frequencies for their dialect. This lad in the article has a real knack for it though, I guess he knows the subject matter pretty well (i.e. knowing the kind of things people will be saying in certain scenarios, the word choice, how they address each other, how the gang hierarchies work etc) and has a good mind for the kind of on-the-fly ciphers that these gangs employ.
- Patrick_Devine 13y ago
  What kept nagging me while reading the article was why aren't law enforcement officials taught to crack these types of codes? If your job is law enforcement, just having a simple understanding of the types of simple cyphers which criminals use seems like it would be invaluable. My next thoughts were a. "Would a reasonable set of law enforcement officials actually be able to learn how a simple cypher worked?", b. "If a large enough percentage of law enforcement could crack those types of codes, would the gang members come up with more complex cyphers?", and c. "How hard is it to smuggle a one time pad into prison?".
- mturmon 13y ago
  You would not have to limit yourself to a frequency attack. You could also match decoded text against a word dictionary.
- maxerickson 13y ago
  Frequency analysis works against a few dozen characters.
  - tripzilch 13y ago
    yeah. gp (and I recommend everybody :) ) should probably try cracking a few substitution ciphers by hand just to see incredibly well frequency analysis really works. like you say, a few dozen characters of ciphertext. and you don't even need the full frequency chart, either. just the top few is sufficient (there's a lot of noise as you go down anyway because of Zipf's law). add knowledge of the top-3 bigrams and trigrams, and you're all set. it's all due to the fact that Shannon discovered, that there's only roughly 1.5 bit of entropy per character in English text. and English is in fact one of the more efficient languages when it comes to this, Dutch or German have even less entropy per character :) I don't know how it compares to Spanish, however. gendered words are basically a type of redundancy checks, so they waste bits in that sense.
    - smcl 13y ago
      I have, but I fail to see how frequency analysis can work on "Everything is fine. Everything is cool here, uh, 15 22 27 31"
specialist 13y ago
Trivial to decode / decrypt. But as Gary Klivans says in the article, you still need to know the vocabulary, culture, etc. to understand the meaning. I read about the British code breakers during WWII. After they decoded (decrypted) messages, they still had to work to understand them. They needed to know the acronyms referring to stuff and places, the units of the quantities, etc. Making up an example, so a line "ABC XYZ TTT 45" might mean send 45 barrels of fuel (TTT) from Boston (ABC) to Atlanta (XYZ).

smcl 13y ago

For this guy yes, but for not necessarily everyone. The messages don't seem to be particularly long so it's unlikely a frequency based attack could work. Also if it is then these guys will not exactly be using the Queen's English so they'll likely have a different letter frequencies for their dialect. This lad in the article has a real knack for it though, I guess he knows the subject matter pretty well (i.e. knowing the kind of things people will be saying in certain scenarios, the word choice, how they address each other, how the gang hierarchies work etc) and has a good mind for the kind of on-the-fly ciphers that these gangs employ.

Patrick_Devine 13y ago
What kept nagging me while reading the article was why aren't law enforcement officials taught to crack these types of codes? If your job is law enforcement, just having a simple understanding of the types of simple cyphers which criminals use seems like it would be invaluable. My next thoughts were a. "Would a reasonable set of law enforcement officials actually be able to learn how a simple cypher worked?", b. "If a large enough percentage of law enforcement could crack those types of codes, would the gang members come up with more complex cyphers?", and c. "How hard is it to smuggle a one time pad into prison?".
mturmon 13y ago
You would not have to limit yourself to a frequency attack. You could also match decoded text against a word dictionary.
maxerickson 13y ago
Frequency analysis works against a few dozen characters.
- tripzilch 13y ago
  yeah. gp (and I recommend everybody :) ) should probably try cracking a few substitution ciphers by hand just to see incredibly well frequency analysis really works. like you say, a few dozen characters of ciphertext. and you don't even need the full frequency chart, either. just the top few is sufficient (there's a lot of noise as you go down anyway because of Zipf's law). add knowledge of the top-3 bigrams and trigrams, and you're all set. it's all due to the fact that Shannon discovered, that there's only roughly 1.5 bit of entropy per character in English text. and English is in fact one of the more efficient languages when it comes to this, Dutch or German have even less entropy per character :) I don't know how it compares to Spanish, however. gendered words are basically a type of redundancy checks, so they waste bits in that sense.
  - smcl 13y ago
    I have, but I fail to see how frequency analysis can work on "Everything is fine. Everything is cool here, uh, 15 22 27 31"

specialist 13y ago

Trivial to decode / decrypt. But as Gary Klivans says in the article, you still need to know the vocabulary, culture, etc. to understand the meaning. I read about the British code breakers during WWII. After they decoded (decrypted) messages, they still had to work to understand them. They needed to know the acronyms referring to stuff and places, the units of the quantities, etc. Making up an example, so a line "ABC XYZ TTT 45" might mean send 45 barrels of fuel (TTT) from Boston (ABC) to Atlanta (XYZ).