Typing The Letters A-E-S Into Your Code? You’re Doing It Wrong
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Re: Typing The Letters A-E-S Into Your Code? You’re Doing It Wrong
#2Hm. I wrote this for our normal blog readers, who live and breathe security stuff, so I don't know how well it'll carry here.
Re: Typing The Letters A-E-S Into Your Code? You’re Doing It Wrong
#3Hm. I wrote this for our normal blog readers, who live and breathe security stuff, so I don't know how well it'll carry here.
It's a fun read. Makes me realize there's a HELLUVA lot more to security than meets the eye, even the eye of someone who's pored over some authentication code. Good submission for HN.
Re: Typing The Letters A-E-S Into Your Code? You’re Doing It Wrong
#4Good read. +1 for Louis CK reference.
A question to start up founders: How do you guys handle security? Do you hire consultants/pen-testers? Do you just copy+paste code from the internet? Do you use whatever framework's components for it?
Re: Typing The Letters A-E-S Into Your Code? You’re Doing It Wrong
#5So, is there much to be gained from encryption anyway? If, as the candidate, I suggested sending a cookie as 'userId=39493&role=user×tamp=1414919&hash=' then would I lose brownie points?
I assume my hash comparison function is constant time (eg. XOR(a[x],b[x])==0), rather than comparing of char-by-char.
Re: Typing The Letters A-E-S Into Your Code? You’re Doing It Wrong
#6[deleted]
Re: Typing The Letters A-E-S Into Your Code? You’re Doing It Wrong
#7Hm. I wrote this for our normal blog readers, who live and breathe security stuff, so I don't know how well it'll carry here.
You blogged the shit outta that post!
Definitely an interesting read even for crypto dilettantes. Perhaps, especially for crypto dilettantes.
I took Rivest's Computer and Network Security class in college and the most important takeaway for me, far outstripping all of the interesting technical content, was "Don't implement crypto."
Re: Typing The Letters A-E-S Into Your Code? You’re Doing It Wrong
#8It's probably worth pointing out: you have the same problems if you're using CFB, OFB, or CTR mode (these are the "stream cipher" modes for DES/AES/whatever that encrypt one byte at a time). There's apocrypha about these modes not being vulnerable to the attack. Bad apocrypha:
Set up an encryptor:
irb> e = OpenSSL::Cipher::Cipher.new('aes-256-ofb')
=> #
irb> e.key = "\x11" * 32
irb> e.iv = "\x00" * 16
irb> d = OpenSSL::Cipher::Cipher.new('aes-256-ofb')
=> #
irb> d.decrypt
irb> d.key = "\x11" * 32
irb> d.iv = "\x00" * 16
irb> ciphertext = (e "a\255N\211XEn\001\347$\275)\311%Ht\2356\254m\b\234z\375\311\006\335\305F\231~\201\243\236\3628w\267\3454"
irb> mask = ("187 she wrote".to_bignum ^ ("A" * 13).to_bignum).to_rawstring
=> "pyva2)$a63.5$"
irb> new_ciphertext = (ciphertext.to_bignum ^ mask.to_bignum).to_rawstring
irb> d "AAAAAAAAAAAAAAAAAAAAAAAAAAA187 she wrote"Re: Typing The Letters A-E-S Into Your Code? You’re Doing It Wrong
#9So, is there much to be gained from encryption anyway? If, as the candidate, I suggested sending a cookie as 'userId=39493&role=user×tamp=1414919&hash= ' then would I lose brownie points? I assume my hash comparison function is constant time (eg. XOR(a[x],b[x])==0), rather than comparing of char-by-char.
No. Like I said, the candidate aced the interview. Holy, he knew what CBC was! Amazing!
Often you don't need confidentiality, and in those cases, HMAC can be a safer bet than a secure encrypted message format. You want to use HMAC though, not a simple hash with a secret key in it.
Re: Typing The Letters A-E-S Into Your Code? You’re Doing It Wrong
#10Hm. I wrote this for our normal blog readers, who live and breathe security stuff, so I don't know how well it'll carry here.
You blogged the shit outta that post! Definitely an interesting read even for crypto dilettantes. Perhaps, especially for crypto dilettantes. I took Rivest's Computer and Network Security class in college and the most important takeaway for me, far outstripping all of the interesting technical content, was "Don't implement crypto."
Man, you had "don't implement crypto" and I was all, that kicks ass. Then you edited it to say "in general", and now I'm sad.