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I'm an engineer with experience in applied cryptography, in particular in Smart Card systems.


May
19
revised What is the recommended replacement for MD5?
typo
May
18
comment Alternatives to HMAC + CBC?
@Luke: If the attacker does not have "direct access to the database" or an equivalent mean, why do you want to encipher each record, and protect their integrity with a keyed scheme? You may need authenticated and enciphered access to the database, and this is NOT the same as authenticating and enciphering each record.
May
18
comment Alternatives to HMAC + CBC?
Also, in the database context: while the confidentiality of each record is protected, the location of updated records is not. And the atomicity of the updates of multiple related records (e.g. update of accounts in a manner preserving the overall balance) is not protected.
May
18
comment Alternatives to HMAC + CBC?
Indeed, the scheme is solid at the record level. I second @Reid's comment: each record's integrity is protected, but the database's integrity is not. Adding an identifier of the record's location in the HMAC helps, by preventing moving records, but it still allows rolling back each record of the database to an earlier state. Even if we link the update of records in some way, the database as a whole can still be rolled back.
May
17
revised What are the potential security impacts of using CRAM-MD5 for Emails, when not using an SSL connection?
Better expalin the main weakness
May
17
revised What are the potential security impacts of using CRAM-MD5 for Emails, when not using an SSL connection?
Polish
May
17
answered What are the potential security impacts of using CRAM-MD5 for Emails, when not using an SSL connection?
May
17
comment What are the potential security impacts of using CRAM-MD5 for Emails, when not using an SSL connection?
The summary of CRAM-MD5 protocol weaknesses on wikipedia is not bad.
May
17
comment Help me describe/identify this challenge-response protocol/algorithm?
@Cybergibbons: in a secure MAC with $k$ possible keys small enough that all keys are enumerable, and $o$ possible outputs, little more than $\lceil k/o\rceil$ examples are necessary to find the key. Here $k=256$ (after vector becomes public), $o=100000$, thus little more than one example is enough. In fairness, an adversary was not supposed to get the program that you reverse-engineered to extract vector; but even considering this, the algorithm is ridiculously weak, see 3a'
May
17
comment Now that quantum computers have been out for a while, has RSA been cracked?
I want to point as worthwhile this opinion and report on the recent events surrounding the D-Wave computer. Especially that part: "Matthias Troyer’s group spent a few months carefully studying the D-Wave problem—after which, they were able to write optimized simulated annealing code that solves the D-Wave problem on a normal, off-the-shelf classical computer, about 15 times faster than the D-Wave machine itself solves the D-Wave problem! "
May
16
revised Help me describe/identify this challenge-response protocol/algorithm?
Expand when even a theorticaly perfect MAC won't do the job
May
16
revised Help me describe/identify this challenge-response protocol/algorithm?
Another, much more devastating attack
May
16
revised Help me describe/identify this challenge-response protocol/algorithm?
Comment on weakness in the usage context
May
16
revised Help me describe/identify this challenge-response protocol/algorithm?
Comment on weakness in the usage context
May
16
revised Help me describe/identify this challenge-response protocol/algorithm?
Rank it
May
16
answered Help me describe/identify this challenge-response protocol/algorithm?
May
16
comment True random numbers generated by sensors
Two problems with use of any hardware as the source of true randomness are 1) hardware fails 2) how much entropy it generates is hard to estimate, and often quite variable. For example, it is entirely conceivable that a particular's iPhone accelerometer is damaged, with constant output of the physical sensor; that an iPhone lays on a steady surface; that apparent noise in the output in that condition (if any) is an artifact of an algorithm, and deterministic; that some factor (temperature, orientation w.r.t. to gravity field..) reduce to nothing the actual entropy available.
May
16
comment SHA-1:Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output?
Additional hint: build (perhaps with a spreadsheet or short program) a Pascal Triangle of appropriate size (perhaps filling it with odds rather than raw number of possibilities); then sum the appropriate terms.
May
15
comment Increased CRC collision probability when adding bits to input message
Indeed, if version 2 was using a different polynomial than V1, there would be collisions between CRC for V1 and V2. I address this issue in the fourth paragraph of my answer.
May
13
revised Increased CRC collision probability when adding bits to input message
typo