9

SHA-1 was SHattered by Stevens et al. They demonstrated that collisions in SHA-1 are practical. They give the first instance of a collision for SHA-1. It is an identical-prefix collision attack that enabled the attacker to forge two distinct PDF documents that have the same SHA-1 hash value. I.e. They extended a given prefix $p$ with two distinct near-...


9

See my paper with Eric Bach, "Factoring with cyclotomic polynomials", where we show that if the cyclotomic polynomial $\Phi_k(p)$ is $B$-smooth for any $p$ dividing $N$, then we can factor $N$ in time polynomial in $\log N$ and $k$ and $B$. In particular this gives a $(p+1)$-method (see the earlier work of Williams) and $(p^2+1)$ method. http://www.ams.org/...


6

Yes, you can use Levin universal search to construct a "universal one-way function" (e.g., these lecture notes). From this one-way function you can then construct symmetric-key encryption primitives (pseudorandom generators, block ciphers, CPA/CCA-secure encryption) using standard theoretical constructions. One-way function $\to$ pseudorandom generator: ...


6

Yes, if the encryption algorithm achieves IND-CPA security (semantic security), this implies that an adversary cannot predict any linear combination of encrypted bits better than random guessing. The easiest way to see this is to note that IND-CPA (left-or-right indistinguishability) implies real-or-random indistinguishability under chosen-plaintext attack:...


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