On some models, operators could achieve a speed of 20 words a minute, and the output ciphertext or plaintext was printed on paper tape.

For example, the plaintext alphabet could be written out in a grid, then every letter in the message replaced by its co-ordinates ( see Polybius square and Straddling checkerboard ).

In turn, these guesses suggest still others ( for example, "< tt > remarA </ tt >" could be "< tt > remark </ tt >", implying < tt > A </ tt >~< tt > k </ tt >) and so on, and it is relatively straightforward to deduce the rest of the letters, eventually yielding the plaintext.

Older systems used techniques such as padding and Russian copulation to obscure information in plaintext that could be easily guessed, and to resist the effects of loss of plaintext on the security of the cryptosystem.

The Rabin cryptosystem was the first asymmetric cryptosystem where recovering the entire plaintext from the ciphertext could be proven to be as hard as factoring.

To obtain this unencrypted file the attacker could search the website for a suitable file, find it from another archive they can open, or manually try to reconstruct a plaintext file armed with the knowledge of the filename from the encrypted archive.

Later attacks, precursors to linear cryptanalysis, could break versions under the known plaintext assumption, first ( Tardy-Corfdir and Gilbert, 1991 ) and then ( Matsui and Yamagishi, 1992 ), the latter breaking FEAL-4 with 5 known plaintexts, FEAL-6 with 100, and FEAL-8 with 2 < sup > 15 </ sup >.

Any putative solution that gave, for any location, the same letter in the proposed plaintext and the ciphertext, could therefore be eliminated.

This helped in testing a possible crib against the ciphertext, as it could rule out a number of cribs and positions, where the same letter occurred in the same position in both the plaintext and the ciphertext.

For these ciphers an attacker should not be able to find the key even if he knows any amount of plaintext and corresponding ciphertext and even if he could select plaintext or ciphertext himself.

Biryukov and Kushilevitz ( 1998 ) published an improved differential attack requiring only 16 chosen-plaintext pairs, and then demonstrated that it could be converted to a ciphertext-only attack using 2 < sup > 12 </ sup > ciphertexts, under reasonable assumptions about the redundancy of the plaintext ( for example, ASCII-encoded English language ).

The plaintext would then appear on one of the other lines, which could be visually located easily, as it would be the only one likely to " read.

The same codebook could be used to " encode " a plaintext message into a coded message or " codetext ", and " decode " a codetext back into plaintext message.

This meant that some possible solutions could quickly be eliminated because of the same letter appearing in the same place in both the ciphertext and the putative piece of plaintext.

John Jay and Arthur Lee devised dictionary codes in which numbers referred to the page and line in an agreed-upon dictionary edition where the plaintext ( unencrypted message ) could be found.

Specifically, if SSL / TLS is not used, then the credentials are passed as plaintext and could be intercepted.

Without knowledge of the key, it should be difficult, if not nearly impossible, to decrypt the resulting ciphertext into readable plaintext.

In other words, an eavesdropper would not be able to improve his or her guess of the plaintext by gaining knowledge of the ciphertext but not of the key.

If the key is truly random, as large as or greater than the plaintext, never reused in whole or part, and kept secret, the ciphertext will be impossible to decrypt or break without knowing the key.

In PGP, these are used by default in conjunction with encryption, but can be applied to the plaintext as well.

Transmission of the password, via the browser, in plaintext means it can be intercepted along its journey to the server.

As with any stream cipher, these can be used for encryption by combining it with the plaintext using bit-wise exclusive-or ; decryption is performed the same way ( since exclusive-or is a symmetric operation ).

A message, the plaintext, may be first encrypted by traditional means, producing a ciphertext.

It exposes to the upper layer an interface for sending and receiving plaintext packets with sizes of up to 32, 768 bytes each ( more can be allowed by the implementation ).

The RED / BLACK concept requires electrical and electronic circuits, components, and systems which handle encrypted ciphertext information ( BLACK ) be separated from those which handle unencrypted classified plaintext information ( RED ).

In cryptography, a substitution cipher is a method of encryption by which units of plaintext are replaced with ciphertext, according to a regular system ; the " units " may be single letters ( the most common ), pairs of letters, triplets of letters, mixtures of the above, and so forth.

However, the keystream must be ( at least ) the same length as the plaintext, and generated completely at random.

Based on this key, it generates a pseudorandom keystream which can be combined with the plaintext digits in a similar fashion to the one-time pad.

Moreover, because of this property, synchronous stream ciphers are very susceptible to active attacks — if an attacker can change a digit in the ciphertext, he might be able to make predictable changes to the corresponding plaintext bit ; for example, flipping a bit in the ciphertext causes the same bit to be flipped in the plaintext.

This should be true for all keys ( there should be no weak keys ), and true even if the attacker can know or choose some plaintext or ciphertext.

For example, if a 128-bit block cipher received separate 32-bit bursts of plaintext, three quarters of the data transmitted would be padding.

ElGamal encryption is probabilistic, meaning that a single plaintext can be encrypted to many possible ciphertexts, with the consequence that a general ElGamal encryption produces a 2: 1 expansion in size from plaintext to ciphertext.

For some chosen-plaintext attacks, only a small part of the plaintext needs to be chosen by the attacker: such attacks are known as plaintext injection attacks.

Gardening can be viewed as a plaintext injection attack.

After inserting spaces, the plaintext is revealed: " Help me I am under attack ".

For example, an attacker who knows that the message contains " Meet Jane and me tomorrow at 3: 30 pm " at a particular point can recover the keystream at that point from the ciphertext and plaintext.

For instance, in English, the plaintext letters E, T, A, O, I, N and S, are usually easy to identify in ciphertext on the basis that since they are very frequent ( see ETAOIN SHRDLU ), their corresponding ciphertext letters will also be as frequent.

Cribs were used by exploiting common formalities in Japanese messages, such as " I have the honor to inform your excellency " and the use of formal, stylized titles ( see known plaintext attack ).

This states that Alice intends a message for Bob consisting of a plaintext encrypted under shared key K < sub > AB </ sub >.

We write out the running key under our plaintext:

When a captured German revealed under interrogation that Enigma operators had been instructed to encode numbers by spelling them out, Alan Turing reviewed decrypted messages and determined that the number “ eins ” (" 1 ") was the commonest string in the plaintext.

The underlying cryptosystem is IND-CPA ( and thus semantically secure under chosen plaintext attack ) if the adversary cannot determine which of the two messages was chosen by the oracle, with probability significantly greater than ( the success rate of random guessing ).

When combined with any secure trapdoor one-way permutation, this processing is proved in the random oracle model to result in a combined scheme which is semantically secure under chosen plaintext attack ( IND-CPA ).

The property of indistinguishability under chosen plaintext attack is considered a basic requirement for most provably secure public key cryptosystems, though some schemes also provide indistinguishability under chosen ciphertext attack and adaptive chosen ciphertext attack.

Indistinguishability under chosen plaintext attack is equivalent to the property of semantic security, and many cryptographic proofs use these definitions interchangeably.

The most common definitions used in cryptography are indistinguishability under chosen plaintext attack ( abbreviated IND-CPA ), indistinguishability under ( non-adaptive ) chosen ciphertext attack ( IND-CCA ), and indistinguishability under adaptive chosen ciphertext attack ( IND-CCA2 ).

For a probabilistic asymmetric key encryption algorithm, indistinguishability under chosen plaintext attack ( IND-CPA ) is defined by the following game between an adversary and a challenger.

However, authenticated encryption can be generically constructed by combining an encryption scheme and a Message Authentication Code ( MAC ), provided that the encryption scheme is semantically secure under chosen plaintext attack and the MAC function is unforgeable under chosen message attack.