# Tag Info

2

For the signatures, hash-based signatures provide a nice solution to your problem: You can use so called hash combiners to instantiate the signature. These are functions that construct a hash function given two or more hash functions and preserve certain properties as long as at least one of the hash function has this property. For example the concatenation ...

3

If you want $N$ serial numbers, your serial numbers will have to use $n$ bits for uniqueness, where $n = \log_2 N$. So if you have 100 bits to use for the serial, you could use 20 to get about a million serials and have 80 bits to use for a cryptographic MAC or signature. Now there are two approaches, the symmetric and the asymmetric. In the symmetric ...

3

If you look at exact security, the height matters. The reason is that it defines the number of OTS key pairs and hence the possible number of one time signatures per MSS key pair. To forge a MSS signature, it is enough to generate a forgery for 1 out of $2^h$ OTS signatures. Hence you get a reduction in the bit security of $h$ bits.

0

You cannot ensure this - at least not against an determined attacker. Depending on the platform the app runs you might get some more assurance (think "TPM with metered boot"), but as soon as the attackers have control over the device they can circumvent it - even when your app is confined in a smartcard or similiar rigidly protected device.

2

SafeCurves lists some ways to compare the security of elliptic curves. Their security criteria are split to "ECDLP security" and "ECC security". Failing the former basically means "there is no way to use this curve securely in general" while the latter "it is difficult to implement this curve securely". None of the (few) BouncyCastle-supported curves that ...

2

You may probably use any curve you like, depending on your special requirements (environment, computational aspects, ...) and the curves implemented by your library (see otus answer refering to some concrete security findings related to specific elliptic curves, and how sensible they are to certain attacks). The reason why the curves are pre-computed, is ...

Top 50 recent answers are included