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Feb
18
answered How can I calculate the SHA-256 “midstate”?
Feb
10
answered Is Common Name encoded in the certificate?
Feb
7
comment How are timestamps verified?
There are several ways to timestamp a PDF file. You can handle it as an opaque blob, and produce an external time stamp (or evidence record). You can also embed the time stamp in the file, because the PDF format includes some provisions for it; such a time stamp can be verified from within Adobe Reader itself. Universign supports both; see: universign.eu/en/web-services
Feb
6
comment What are the practical differences between 256-bit, 192-bit, and 128-bit AES encryption?
@DanNeely: a block cipher with 256-bit keys is supposed to offer resistance up to work factor $2^{256}$; there should not exist any (theoretical) attack which would be less expensive. An attack with cost $2^{200}$ is considered to be a "break" for a block cipher with a 256-bit key; but not for a block cipher with a 128-bit key, for which we "only" require resistance up to $2^{128}$ operations. The extra rounds help in obtaining that level of resistance.
Feb
6
answered How are timestamps verified?
Feb
6
answered How to account for moore's law in estimating time-to-crack?
Feb
2
reviewed Approve commitments tag wiki excerpt
Feb
2
comment Is RSA of a random nonce with no padding safe?
@Gilles: if padding is deterministic, and you encrypt the same $K$ (padded to $\pi(K)$) for three different recipients, with $e = 3$, then you send the value $\pi(K)^3$ modulo $n_1$, $n_2$ and $n_3$. By the Chinese Remainder Theorem, this is sufficient to rebuild $\pi(K)$ modulo $n_1n_2n_3$, and since $\pi(K) \lt n_i$, the modulo disappears. This is the historical justification for using $e = 65537$ instead of $e = 3$, but the real issue is that a deterministic padding for RSA encryption is definitely unsafe. You MUST have a random padding.
Feb
2
awarded  encryption
Feb
1
answered Is RSA of a random nonce with no padding safe?
Feb
1
answered How can I convert a DER ECDSA signature to ASN.1?
Feb
1
awarded  Good Question
Feb
1
awarded  Nice Answer
Jan
30
comment Salts, how does the script know what the salt is?
Actually, for most password-related salt usages, what we need is just that salt values are distinct from each other. Unbiased selection in a big enough space is sufficient to achieve uniqueness. Dates are not bad as themselves -- as long as you never choose two salts during the same second, and you take care never to repeat dates, even when the system administrator resets the clock.
Jan
27
comment What is the best way to send two floating point numbers to a server on the internet from a small device such as an arduino?
@DavyLandman: what I described is a single block encryption, which does not use any encryption mode -- it provides the desired properties only because it is a single block encryption, and has the specific format and rules that I mandate. CBC encryption handles longer messages but does not provide a MAC by itself; and CBC requires an IV which MUST be selected randomly and uniformly, and a new IV MUST be generated for each message. CBC is needy. I suggest you investigate EAX, which includes a MAC and has lighter IV needs (a counter suffices).
Jan
27
awarded  Nice Answer
Jan
26
comment What is the best way to send two floating point numbers to a server on the internet from a small device such as an arduino?
@DavyLandman: without some kind of memory, there is no way for the device to send messages which will resist malicious reordering by Eve -- unless you go with a two-directional protocol, in which the server interactively exchanges messages with the device: at that point, things become really complex, both to implement and to analyze.
Jan
26
revised What is the best way to send two floating point numbers to a server on the internet from a small device such as an arduino?
edited body
Jan
26
answered What is the best way to send two floating point numbers to a server on the internet from a small device such as an arduino?
Jan
25
reviewed Approve Stretching a random seed to maximize entropy