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


Jan
1
revised What is the SSL private key file format?
Fix length encoding
Jan
1
revised What is the SSL private key file format?
avoid a repetition
Dec
31
revised What is the SSL private key file format?
BER/DER-TLV supports length above 0xFFFFFFFF; other standards do not.
Dec
31
comment What is the SSL private key file format?
@neubert: ah, now I see why 30 is the ASN.1 sequence tag; and 02 is int. $\;$ Thanks for that!
Dec
31
revised What is the SSL private key file format?
Hopefully less mixup between ASN.1, BER and DER; add reference
Dec
31
revised What is the SSL private key file format?
Expand how-to
Dec
31
comment What is the SSL private key file format?
If the encoding is per RFC3447 appendix C: I wonder you go from this to the first byte 30 of the bytestring? I never managed to get that part!
Dec
31
revised What is the SSL private key file format?
Answer "how do I convert those numbers to the private.key format?"
Dec
31
answered What is the SSL private key file format?
Dec
25
comment Security concern about reducing hash value using modulo operation
See this answer
Dec
24
comment power consumption in a XOR
Since a difference in energy is asked, that is proportional to a duration, which could be anything from a clock cycle (perhaps down to 10ns in some areas of the Smart Card) to months. That also depends tremendously on where in the Smart Card the XOR occurs (is that in the CPU ALU? An AES block? Some bus encryption unit?); the silicon technology; and exactly what one accounts as radiated. Also, it can happen that whatever quantity is available to the attacker depends more on change of state, than on the state itself.
Dec
22
revised On-the-fly computation of AES Round Keys for decryption?
Clarify that it is the reversed key schedule (not decryption) that uses the direct AES SBox
Dec
22
comment On-the-fly computation of AES Round Keys for decryption?
@Craig McQueen: you are absolutely right! Fixed the answer accordingly.
Dec
22
revised On-the-fly computation of AES Round Keys for decryption?
Fix per comment
Dec
20
comment Are there signatures that don't have subliminal channels?
Indeed. In addition to PKCS#1v1.5, there are ISO/IEC 9796-2 schemes 1 and 3 (with defined-in-advance parameters such as choice of hash), and the defunct ISO/IEC 9796(-1), which are RSA-based signature schemes such that a single valid signature exists for any signed message, implying there is no subliminal channel.
Dec
14
comment N way collision of hashes
The answer is fine if we are content with the statement's For a collision $H(A_1) = H(A_2)$, the number of queries is $T^{1/2}$. $\;$ But this is less than precise; rather, the number of queries to reach an $n$-collision with odds $1/2$ (or any fixed probability in range $]0,1[$ ) is $\mathcal O(T^{1-1/n})$ when $T$ goes to infinity.
Dec
14
revised N way collision of hashes
base-2 log is used
Dec
14
reviewed Approve N way collision of hashes
Dec
12
comment Crack RSA with imaginary algorithm
It is not evident that the algorithm in the first comment succeeds. In fact, if we had $2^{k\cdot e}\bmod N=1$ for some $k<100$, then the algorithm would fail its goal. $\;$ The canonical answer to this question uses random numbers, rather than successive powers of two, in order to avoid that issue.
Dec
12
comment 2048-bit RSA Decryption
Right. Notice that if $e=2^{16}+1$, the cost of brute force is $\approx 17\cdot M$ modular multiplications; when the answer's algorithm uses about $17\cdot4\sqrt M$ in the first phase, and $k\cdot4\sqrt M$ in the second phase, for some $k$ depending on the modular inverse algorithm, certainly $k<2\log_2(N)=4096$, which is a huge improvement, trouncing the $4\cdot10^{20}$ asked in the question. $\;$ As an aside, we can simplify things slightly by merging the two phases: we can search for $(M^e)\cdot((a^e)^{-1})\bmod N$ in the table right after entering $a^e\bmod N$ in the table.