# Tag Info

1

“Randomly derived” is not standard phrasing and I suspect that it isn't what the author meant to write. From context, what is necessary here is to have a distinct key for each message. This can be achieved either by randomly generating a key (I think that's what the author meant to write) or by deriving a key using a key derivation function with a unique ...

0

I think what you are looking for is impossible. To see this, let's formalize things a bit: You have an oracle (the HW token) $T(Q)=[x]Q$ which computes a scalar product of any given input point with a secret scalar. You have an integer (or a byte sequence) $t$ - the tweak - and you have a public point $Q'$ from your partner as well as of course a standard ...

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This is broken, because possession of Epriv (a function of the public tweak value) allows calculation of the output of tokenECDH(Epub) given knowledge of tokenPub (another public value). This is stupid obvious now, but it took several days to figure it out.

5

You should never re-use a salt, and you should especially not hardcode it for your entire application! A salt has several purposes, including the one you mentioned (defeating rainbow table attacks and others based on precomputation). However, a salt also prevents an attacker from trying to break multiple users' passwords at once. If you use a salt that is ...

1

No, it uses a specific type of algorithm called a key schedule. Unlike a KDF, it is not designed to be slow (in the case of a password-based KDF) or to be irreversible. The requirements of a key schedule are quite simple. Whereas a KDF might need to expand a key into a number of keys such that knowledge of any one key does not reveal knowledge of the master ...

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It appears that this is a duplicate question. See: How to salt PBKDF2, when generating both an AES key and a HMAC key for Encrypt then MAC? Derive both MAC and AES keys from same PBKDF2? Deriving 2 keys using HKDF

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