B-Con

2,174 reputation

1418

bio	website	bradconte.com
	location	Texas, USA
	age	25
visits	member for	1 year, 9 months
	seen	7 hours ago
stats	profile views	18

I'm a software engineer. My specific interests are Cryptography and computer security. I graduated from UC Davis with B.S.s in C.S. and pure math.

My website: http://bradconte.com

	2,174 reputation	bio	website	bradconte.com	visits	member for	1 year, 9 months
1418 badges		location	Texas, USA		seen	7 hours ago

summary answers questions tags badges favorites bounties reputation activity

242 Actions

suggestions reviews revisions comments badges posts accepts all

Apr 9	comment	Does encrypting twice using the same block cipher produce a security weakness? @Jalaj: DES has weak keys that cause encryption and decryption to behave the same, so double encryption will actually yield the original plaintext. Modern block ciphers avoid this sort of weakness, but without having a specific cipher to talk about, his original caution makes sense: Double encrypting with the same key is not unconditionally safe. Best practice is probably to always use separate keys.
Apr 6	revised	Predicting PRNG given some of its previous output edited tags
Apr 6	comment	Crypto-Compression Algorithms? How are you going to decrypt it without that data? I'm not worried about the encryption part, but rather the decryption part. Once you walk away from the data, anyone who wants to decrypt it will either need access to some unknown value or they will not. If they do, then for all effective purposes you are using some form of a key for the encryption/decryption process. If they do not, you're using obfuscation, not encryption, and they will be able to reverse it.
Apr 5	answered	Crypto-Compression Algorithms?
Apr 5	comment	Why is the IV passed in the clear when it can be easily encrypted? @Adam: To be complete, if the IV is unpredictably random then it does not need to be encrypted to achieve semantic security.
Apr 5	comment	Encryption algorithm that produces dummy output on incorrect passwords FPE ensures that all keys will always decrypt to plaintext that was considered valid at encryption time, which is what the question asked. The future attacker is assumed to know the PT domain, but FPE negates that advantage. They may also know more about the PT than just the domain, as I outlined, but the OP's question seems about the PT domain, not message-specific knowledge (see the account number example). For very complicated domains, defining it carefully and using FPE efficiently would be very difficult. But it's still a theoretical construction that closely matches the OP's question.
Apr 4	revised	Encryption algorithm that produces dummy output on incorrect passwords Clarity.
Apr 4	revised	Can you make a hash out of a stream cipher? Typo.
Apr 4	answered	Can you make a hash out of a stream cipher?
Apr 4	revised	Encryption algorithm that produces dummy output on incorrect passwords Parenthetically set aside the 3rd paragraph.
Apr 4	answered	Encryption algorithm that produces dummy output on incorrect passwords
Apr 3	comment	Can you make a hash out of a stream cipher? @Illmari: You are correct, I only sought to address one straight-forward construction. I edited my answer to emphasis that. @ Jalaj: I was also downvoted, so it seems like someone disliked our answers. (Maybe because they were more informative and less conclusive.)
Apr 3	revised	Can you make a hash out of a stream cipher? Added clarity on the scope of my answer.
Apr 2	awarded	Enthusiast
Apr 1	awarded	Critic
Apr 1	revised	How secure is AES-256? typos
Apr 1	answered	How secure is AES-256?
Apr 1	awarded	Organizer
Apr 1	revised	Can a user of a password-protected Wi-Fi sniff on other user's communication? edited tags
Apr 1	comment	How does one attack a two-time pad (i.e. one time pad with key reuse)? If string1[i] == string2[i], that only means that C2[i] == C3[i] (and thus M2[i] == M3[i]). You can check that fact without doing any of those XOR operations. And XORing string1 by C2 gives you back C1 XOR "space", which, at a glance, doesn't seem to be related to key[i]. I haven't looked at that EC assignment for the class in any detail yet, but I think you're supposed to use the fact that XORing by "space" only changes the case of the original character. You might use that fact to analyze the XOR or two plaintext messages, which you obtain by XORing their two respective ciphertexts.