Impact of quantum
computing on encryption
Security of encryption and hashing
algorithm rely on computational
unfeasibility of solving some classes of hard mathematical problems in
reasonable time and with finite / cost effective computation resources.
Quantum computing, based on quantum bits (qbits) which can exist in
superpositions of states, provides breakthrough performances in
solving some classes of hard mathematical problems over classic
computing methods, based on binary digital electronic architecture;
the impact of this performance improvement must be carefully evaluated
to assess
security of existing cipher and hash functions in a scenario where
quantum computers will be available.

Under
current understandings, the impact of increasingly more powerful
quantum computers with increasingly larger number of qbits has very
different degrees of impact on feasibility to reduce / break security
of algorithms commonly employed in symmetrickey
or publickey cryptography. 

Quantum
computing and symmetrickey encryption algorithms
To
preserve data secrecy, symmetrickey cryptography rely on a shared
secret element (password / passphrase, keyfile, biometric data, or
combinations of more factors as in twofactor authentication) between
two or more parties.
The need to share this element, needed by receiver for decryption, is
the main
disadvantage of (secret) symmetrickey cryptography solutions over
publickey cryptography solutions.
Algorithms in use in PeaZip
PeaZip currently supports only symmetickey
encryption mechanisms, using password / passphrase and optionally
twofactor authentication (password / passphrase + key file), which
under current understandings are quite
secure against attacks by
arbitrarily sized quantum computers.
Attacks on symmetric
encryption algorithms using quantum computers
Grover's quantum algorithm is the bestpossible known attack for most
of current generation symmetric encryption algorithms (and hash
functions), providing  for NPcomplete problems  a quadratic speedup
over a classic computing based bruteforce search.
Security of symmetric
encryption algorithms from quantum computing methods

As
a general rule, doubling the size of a symmetric key
can
effectively make up for the increase of efficiency of Grover's
algorithm over classic bruteforcing, and defeat the purpose of
these attacks. 

IUnder those premises, in example
AES 256 bit could be considered equivalent in security (when
arbitrarily large quantum computers are available, using Grover
algorithm over the 256 bit key space) to AES 128 bit (for
classic computers, using classic computing bruteforce over the 128 bit
key space)  which means 256 bit key size is considered secure even in
case of quantum computing attack, under current understandings.
Same holds true for other symmetric key ciphers like DES, Blowfish,
Twofish, and Serpent.
While a quadratic speedup (providing a sufficiently powerful quantum
computer is available) is an huge performance improvement, it is
nowhere near a complete breakthrough as polynomial time solution
provided by Shor's algorithm is for publickey encryption systems, so
postquantum symmetric
cryptography is thought to not need to differ significantly from the
current generation.
Read more about symmetickey encryption algorithms supported by PeaZip:
Rijndael/AES
(implemented as AES128 and AES256 in 7Z, ARC, RAR, PEA, and ZIP
standards),
and Twofish and Serpent ciphers
(implemented for ARC and PEA
standards).
Read more about cryptographically
secure hash function
Learn more: Grover's
algorithm
Quantum
computing and publickey encryption algorithms
Publickey
encryption systems are currently extremely popular, as they
simplify key exchange task: anyone can encrypt a message using a public
key released by a receiver, but only receiver's private key can decrypt
messages protected by its public key.
Unfortunately, most ones of currently popular publickey algorithms are
susceptible of being efficiently broken by a large enough quantum
computer.
Attacks on public key
encryption algorithms using quantum computing

Shor's quantum algorithm runs in
polynomial time to solve hard
mathematical problems used in most common publickey encryption
(integer
factorization problem, discrete logarithm problem, ellipticcurve
discrete logarithm problem), rather than in exponential or
subexponential time as the best, most efficient classic algorithms. 

Experimental publickey algorithms relying on problems not efficiently
simplified by Shor's algorithm or other quantum algorithms, being both
reasonably safe under classic computing and quantum computing based
attacks, is currently an active research topic in cryptography.
PeaZip currently does not
support publickey encryption methods, only
symmetric (secret) key encryption  keys (passwords, keyfiles) needs
to be privately, securely shared with receiver for decryption to take
place.
Learn more: Shor's
algorithm
.
Quantum
cryptography

Please note that quantum
cryptography is a
separate topic, studying how to
apply quantum phenomena to cryptography in order to achieve
secrecy and detect
eavesdropping, rather than analyzing how
quantum computers
characteristics affects safety (in terms of computational
feasibility
of attacks or bruteforcing) of encryption / hashing algorithms  the
topic discussed in this page and properly named postquantum
cryptography 
Learn more about PEA encryption
utility, how to protect files and
folders, how to securely share
files with email or cloud, and how
to try to open unreadable files.
Synopsis: Postquantum
computing cryptanalisys of cryptography methods used in PeaZip.
Security of AES, Twofish and Serpent symmetric key encryption attacked
by Grover algorithm. Impact of quantum computing attacks on public key
encryption methids with Shor algorithm. Secure key size for quantum
computing attacks.
Topics: impact of
quantum computing on symmetyric
key cryptography algorithms employed in PeaZip
PeaZip > FAQ >
Postquantum computing cryptography analysis of PeaZip
