Factoring
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FACTORING: integer factorisation problem
Definition: Given a positive integer
, find its prime factorisation
where the pi are pairwise distinct primes and ei > 0.
Reductions: SQRT ≡P FACTORING, RSAP ≤P FACTORING, Strong-RSAP ≤P FACTORING
Algorithms: The best known algorithm for FACTORING is the Number Field Sieve which has complexity LN(1 / 3,c) for some constant c.
Use in cryptography:
SQRT: square roots modulo a composite
Definition: Given a composite positive integer
and a square a modulo n, find a square root
of a modulo n, this is, an integer x such that
.
Algorithms: The best known algorithm for SQRT is to actually solve the FACTORING problem.
Use in cryptography: Rabin encryption
History:
References:
CHARACTERd: character problem
Definition: Let n and d be positive integers. Divise
an algorithm which given
computes
χ(x) where χ is a non-trivial character of
of order d.
Reductions:
Algorithms:
Use in cryptography: Undeniable Signatures
History:
Remark: This can be seen as a generalisation of the quadratic residuosity problem.
References:
- J. Monnerat, S. Vaudenay, Undeniable Signatures Based on Characters: How to Sign with One Bit, PKC 2004.
MOVAd: character problem
Definition: Let
,
and χ a hard character of order d on
. Given s pairs (αi,χ(αi)), where
for all
and
, compute χ(x).
Reductions: MOVAd ≤ CHARACTERd in some cases (as the characters in each cases may be independant), MOVAd ≤ CYCLOFACTd
Algorithms:
Use in cryptography: Undeniable Signatures
History:
Remark:
References:
- J. Monnerat, S. Vaudenay, Undeniable Signatures Based on Characters: How to Sign with One Bit, PKC 2004.
CYCLOFACTd: factorisation in
Definition: Let θ be a dth root of unity. Let σ be an element of
, find the factorisation of θ.
Reductions: CYCLOFACTd ≡ FACTORING for d = 1,2,3,4.
Algorithms:
Use in cryptography:
History:
Remark:
References:
- J. Monnerat, S. Vaudenay, Undeniable Signatures Based on Characters: How to Sign with One Bit, PKC 2004.
FERMATd: factorisation in
Definition: Let θ be a dth root of unity. Let
be such that
for some
. Given n, find π.
Reductions: FERMATd ≤ CYCLOFACTd for d = 1,2,3,4, FERMAT3 ≡ Finding a square root of − 3 modulo n, for some n for which − 3 is a quadratic residue, FERMAT4 ≡ Finding a square root of − 1 modulo n, for some n for which − 1 is a quadratic residue.
Algorithms:
Use in cryptography:
History:
Remark:
References:
- J. Monnerat, S. Vaudenay, Undeniable Signatures Based on Characters: How to Sign with One Bit, PKC 2004.
RSAP: RSA problem
Definition: Given a positive integer n which is the product of at least two primes, an integer
e coprime with
and an integer c, find an integer m such that
.
Reductions: RSAP ≤P FACTORING, Strong-RSAP ≤P RSAP
Algorithms: The best known attack is to use the reduction to FACTORING. However, there are a number of results which either point to seperation between the RSA Problem and FACTORING, or point to their equivalence. The issue of this seperation is a topic of current research.
Use in cryptography: The RSA cryptosystem.
History:
References:
Strong-RSAP: strong RSA problem
Definition: Given a positive integer n which is the product of at least two primes and an integer c,
find an odd integer
and an integer m such that
.
Reductions: Strong-RSAP ≤P FACTORING, Strong-RSAP ≤P RSAP
Algorithms: Again the best known attack is reduction to the FACTORING problem.
Use in cryptography: Cramer-Shoup signatures
History:
References:
Difference-RSAP: Difference RSA problem
Definition: Given a positive integer n which is the product of at least two primes, an element
and m-1 pairs (xi,yi) such that
, for chosen xi,
find a new pair (xm,ym) such that
.
Reductions: Difference-RSAP ≤P FACTORING, Difference-RSAP ≤P RSAP
Algorithms: Again the best known attack is reduction to the FACTORING problem.
Use in cryptography:
History:
References:
- M. Naor, On Cryptographic Assumptions and Challenges, Invited paper, Crypto 2003.
Partial-DL-ZN2P: Partial Discrete Logarithm problem in
Definition: Given a positive integer n such that n=pq with p=2p'+1 and q=2q'+1, for prime numbers p,p',q,q', an element
of maximal order in
and h = gamod n2 for some
, find an integer x such that x = a(mod n).
Reductions: Partial-DL-ZN2P ≤P FACTORING
Algorithms: The problem is not harder than the FACTORING problem.
Use in cryptography: Homomorphic public key encryption, public key encryption with double trapdoor decryption mechanism
History:
References:
- P. Paillier, Public-Key Cryptosystems Based on Composite Degree Residuosity Classes, Eurocrypt 1999.
- E. Bresson, D. Catalano, D. Pointcheval, A Simple Public Key Cryptosystem with a Double Trapdoor Decryption Mechanism and Its Applications, Asiacrypt 2003.
DDH-ZN2P: Decision Diffie-Hellman problem over
Definition: Given a positive integer n such that n=pq with p=2p'+1 and q=2q'+1, for prime numbers p,p',q,q', an element
of maximal order in
, elements X = gxmod n2, Y = gymod n2, for some
, and
, decide whether Z = gxymod n2.
Reductions: DDH-ZN2P ≤P FACTORING
Algorithms: The problem is not harder than the FACTORING problem.
Use in cryptography: Public key encryption with double trapdoor decryption mechanism
History:
References:
- E. Bresson, D. Catalano, D. Pointcheval, A Simple Public Key Cryptosystem with a Double Trapdoor Decryption Mechanism and Its Applications, Asiacrypt 2003.
Lift-DH-ZN2P: Lift Diffie-Hellman problem over
Definition: Given a positive integer n such that n=pq with p=2p'+1 and q=2q'+1, for prime numbers p,p',q,q', an element
of maximal order in
, elements X = gxmod n2, Y = gymod n2, for some
, and Z = gxymod n, find Z' = gxymod n2.
Reductions: Partial-DL-ZN2P ≤P Lift-DH-ZN2P
Algorithms:
Use in cryptography: Public key encryption with double trapdoor decryption mechanism
History:
References:
- E. Bresson, D. Catalano, D. Pointcheval, A Simple Public Key Cryptosystem with a Double Trapdoor Decryption Mechanism and Its Applications, Asiacrypt 2003.
EPHP: Election Privacy Homomorphism problem
Definition: Given a fixed small prime e, a prime p such that e | (p − 1), and a prime q such that
let n = pq and let
such that e divides the order of g. We refer to the group generated by g as G.
The EPHP problem is to decide for
and
whether w = gv + er for some
. This should be done with a probability significantly greater than (e − 1) / e.
Reductions: EPHP ≤P Partial-DL-ZN2P ≤P FACTORING
Algorithms:
Use in cryptography: Homomorphic public key encryption and electronic voting protocols
References:
- Kenneth R. Iversen: A Cryptographic Scheme for Computerized Elections. CRYPTO 1991: 405-419
AERP: Approximate e-th root problem
Definition: Given a positive integer n which is of the form p2q, with p, q prime and | n | = 3k, an integer
and a
, find an integer x such that
, where
.
Algorithms: The best known attack is to use the reduction to FACTORING.
Use in cryptography: The ESIGN signature scheme.
History:
References:
- Jacques Stern: Why Provable Security Matters? EUROCRYPT 2003: 449-461
l-HENSEL-RSAP: l-Hensel RSA
Definition: Given N = pq, e coprime with φ(N), and xe(mod N) for a random integer 1 < x < N, compute
.
Reductions: 2-HENSEL-RSAP ≡P RSAP for a public exponent e coprime with N.
3-HENSEL-RSAP ≡P CLASS for the public exponent e = N.
Algorithms:
Use in cryptography: Public-key encryption
References:
- Dario Catalano, Phong Q. Nguyen, and Jacques Stern, The Hardness of Hensel Lifting: The Case of RSA and Discrete Logarithm, ASIACRYPT 2002, LNCS 2501, pp. 299–310.
DSeRP: Decisional Small e-Residues in
Definition: Given a positive integer n such that n=pq for prime numbers p,q and an integer e>2 such that gcd(e,n(p − 1)(q − 1)) = 1, distinguish the distributions
and
.
Reductions: DSeRP ≤P RSAP ≤P FACTORING
Algorithms:
Use in cryptography: Semantically secure public key encryption from Paillier-related assumptions
History:
References:
- D. Catalano, R. Gennaro, N. Howgrave-Graham, P. Nguyen, Paillier's Cryptosystem Revisited, ACM-CCS 2001.
DS2eRP: Decisional Small 2e-Residues in
Definition: Given a positive integer n such that n=pq for prime numbers p,q such that p = q = 3mod 4 and an integer e such that gcd(e,n(p − 1)(q − 1)) = 1 and | n | / 2 < e < | n | , distinguish the distributions
and
.
Reductions: DS2eRP ≤P FACTORING
Algorithms:
Use in cryptography: Semantically secure public key encryption mixing Paillier and Rabin functions
History:
References:
- D. Galindo, S. Martin, P. Morillo, J. L. Villar, A Practical Public Key Cryptosystem from Paillier and Rabin Schemes, Public Key Cryptography 2003.
- K. Kurosawa, T. Takagi, Some RSA-Based Encryption Schemes with Tight Security Reduction, Asiacrypt 2003.
DSmallRSAKP: Decisional Reciprocal RSA-Paillier in
Definition: Given a positive integer n such that n=pq for prime numbers p,q, an element α such that (α / p) = (α / q) = − 1, an integer e such that | n | / 2 < e < | n | , distinguish the distributions
and
.
Reductions: DSmallRSAKP ≤P FACTORING
Algorithms:
Use in cryptography: Semantically secure public key encryption from Paillier-related assumptions
History:
References:
- K. Kurosawa, T. Takagi, Some RSA-Based Encryption Schemes with Tight Security Reduction, Asiacrypt 2003.
HRP: Higher Residuosity Problem
Definition: Let n and a be positive integers such that
. Given
, decide whether there exists y such that ya = x.
Algorithms: The best known <= algorithm is to factor n first. There are algorithms solving this problem efficiently when the factorization of n is known.
Use in cryptography: Convertible Group Signatures, Public Key Encryption.
History:
Remark: The special case a = 2 corresponds to the quadratic residuosity problem.
References:
- S.J. Kim, S.J. Park, D.H. Won, Convertible Group Signatures, Proceedings of Asiacrypt '96, p.311-321.
- D. Naccache and J. Stern, A New Public Key Cryptosystem Based on Higher Residues, ACM Conference on Computer and Communications Security, 1998, p. 59-66.
- B. Pfitzmann, M. Schunter, Asymmetric Fingerprinting, Proceedings of Eurocrypt '96, p. 84-95.
ECSQRT: Square roots in elliptic curve groups over
Definition: Let
be the elliptic curve group over
. Given a point
. Compute all points
such that 2P = Q.
Reductions: ECSQRT ≡P FACTORING
Algorithms: The best algorithm for ECSQRT is to solve the FACTORING problem.
Use in cryptography: Public Key Encryption
History:
References:
- B. Meyer, V. Müller, A Public-Key Cryptosystem Based on Elliptic Curves over
Equivalent to Factoring. Proceedings of Eurocrypt '96, p. 49-59.
RFP: Root Finding Problem
Definition: Compute one (all) root(s) of a polynomial f(x) over the ring
, where n = pq is the product of two large primes..
Reductions: RFP ≡P FACTORING whenever f(x) has at least two different roots.
Algorithms: The best algorithm for RFP is to solve the FACTORING problem.
Use in cryptography: Public key encryption and signature schemes
History:
References:
- J. Schwenk and J. Eisfeld, Public Key Encryption and Signature schemes based on Polynomials over
. Proceedings of Eurocrypt '96, p. 60-71.
phiA: PHI-Assumption
Preliminaries and notation: Let PRIMESa be the set of all primes of length a and Ha be the set of the composite integers that are product of two primes of length a.
We say that a composite integer m φ-hides a prime p if p | φ(m).
Denote by Hb(m) the set of b-bit primes p that are φ-hidden by m, and denote by
the set PRIMESb − Hb(m).
Definition: φ-Hiding Assumption:
such that:
-gate circuits C,
.
φ-Sampling Assumption:
such that:
there exists a sampling algorithm S() such that for all k-bit primes p, S(p) outputs a random kf-bit number
that φ-hides p together with m's integer factorization.
Reductions:
Algorithms:
References:
- C. Cachin, S. Micali and M. Stadler, Computationally Private Information Retrival with Polylogarithmic Communication, EUROCRYPT 1999, LNCS 1592, pp. 402-414.
C-DRSA: Computational Dependent-RSA problem
Definition: Given (N,e) as above and
find (a + 1)e(mod n) where α = ae(mod n).
Reductions: C-DRSA <P RSA. It also holds: RSA ≡P C-DRSA + E-DRSA
Use in cryptography: DRSA-2 encryption scheme by Pointcheval (see the reference below)
References:
- D. Pointcheval, New Public Key Cryptosystems Based on the Dependent-RSA Problems, EUROCRYPT 1999, LNCS 1592, pp. 239-254.
D-DRSA: Decisional Dependent-RSA problem
Definition: Given (N,e) as above,
distinguish if γ = (a + 1)e(mod n) or γ = ce(mod n) where a,c are taken at random in
.
Reductions: D-DRSA <P C-DRSA, D-DRSA <P E-DRSA.
Algorithms: The gcd technique seems to be the best known attack against the D-DRSA problem and is impractical as soon as the exponent e is greater than 260. Which leads to the following conjecture: D-DRSA is intractable as soon as the exponent e is greater than 260, for large enough RSA moduli.
Use in cryptography: DRSA encryption scheme by Pointcheval.
References:
- D. Pointcheval, New Public Key Cryptosystems Based on the Dependent-RSA Problems, EUROCRYPT 1999, LNCS 1592, pp. 239-254.
E-DRSA: Extraction Dependent-RSA problem
Definition: Given (N,e) as above and
and
, find a(mod n).
Reductions: E-DRSA <P RSA. It also holds: RSA ≡P C-DRSA + E-DRSA
Use in cryptography:
References:
- D. Pointcheval, New Public Key Cryptosystems Based on the Dependent-RSA Problems, EUROCRYPT 1999, LNCS 1592, pp. 239-254.
DCR: Decisional Composite Residuosity problem
Definition: Given a composite n and an integer z, decide if z is a n-residue modulo n2 or not, namely if there exists y such that z = yn(mod n2).
Reductions: DCR ≡P DCRC <PCRC <P FACTORING.
Use in cryptography: Paillier's cryptosystem
References:
- P. Paillier, Public-Key Cryptosystems Based on Composite Degree Residuosity Classes, Eurocrypt 1999.
CRC: Composite Residuosity Class problem
Definition: Denote by
the set of elements of order nα and by B their disjoint union for
where λ = λ(n) is the Carmichael's function taken on n.
Given a composite n and
, compute the n-residuosity class of w with respect to g: [w]g.
Use in cryptography:
References:
- P. Paillier, Public-Key Cryptosystems Based on Composite Degree Residuosity Classes, Eurocrypt 1999.
DCRC: Decisional Composite Residuosity Class problem
Definition: Denote by
the set of elements of order nα and by B their disjoint union for
where λ = λ(n) is the Carmichael's function taken on n.
Given a composite n,
, decide wether x = [w]g or not.
Reductions: DCRC <PCRC <P FACTORING.
Use in cryptography:
References:
- P. Paillier, Public-Key Cryptosystems Based on Composite Degree Residuosity Classes, Eurocrypt 1999.
GenBBS: generalised Blum-Blum-Shub assumption
Definition: Given a composite positive integer
and a sequence
to distinguish
from a random r2(mod n).
Reductions: GenBBS ≤P FACTORING
Algorithms: The best known algorithm for GenBBS is to actually solve the FACTORING problem.
Use in cryptography: Timed commitments.
History:
References: D. Boneh and M. Naor, `Timed commitments', CRYPTO 2000.
