A set of reverse rounds are applied to transform ciphertext back into the original plaintext using the same encryption key.

Each bit or character from the plaintext is encrypted by a modular addition with a bit or character from a secret random key ( or pad ) of the same length as the plaintext, resulting in a ciphertext.

By contrast, in a substitution cipher, the units of the plaintext are retained in the same sequence in the ciphertext, but the units themselves are altered.

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.

Symmetric-key algorithms are a class of algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of ciphertext.

If it is any smaller, more than one plaintext may encrypt to the same ciphertext.

In a simple substitution cipher, each letter of the plaintext is replaced with another, and any particular letter in the plaintext will always be transformed into the same letter in the ciphertext.

If an attacker knows the IV ( or the previous block of ciphertext ) before he specifies the next plaintext, he can check his guess about plaintext of some block that was encrypted with the same key before ( this is known as the TLS CBC IV attack ).

The last partial block of plaintext is XORed with the first few bytes of the last keystream block, producing a final ciphertext block that is the same size as the final partial plaintext block.

This characteristic of stream ciphers makes them suitable for applications that require the encrypted ciphertext data to be the same size as the original plaintext data,

At the end of the stack of rotors was an additional, non-rotating disk, the " reflector ," wired such that the input was connected electrically back out to another contact on the same side and thus was " reflected " back through the three-rotor stack to produce the ciphertext.

Both the input ( plaintext ) and output ( ciphertext ) are the same length ; the output cannot be shorter than the input — this follows logically from the Pigeonhole principle and the fact that the cipher must be reversible — and it is undesirable for the output to be longer than the input.

* The reason for confusion is exactly the same as for diffusion: changing one bit of the key changes several of the round keys, and every change in every round key diffuses over all the bits, changing the ciphertext in a very complex manner.

The Meet-in-the-Middle attack attempts to find a value using both of the range ( ciphertext ) and domain ( plaintext ) of the composition of several functions ( or block ciphers ) such that the forward mapping through the first functions is the same as the backward mapping ( inverse image ) through the last functions, quite literally meeting in the middle of the composed function.

Because the cipher doesn't change any of the characters, the ciphertext will have exactly the same letter frequencies as the underlying plaintext.

The skew this causes to the output frequency distribution is smeared by the fact that it is quite possible that ' EE ' and ' QQ ' map to the same ciphertext character, but nevertheless the distribution is not flat.

To decipher the text, the recipient simply hands the same key to the stream cipher to produce an identical keystream and XORs it with the ciphertext, resulting in the original message.

To decipher the ciphertext, the same key would be again combined character by character, producing the plaintext.

In modern terminology, a Vernam cipher is a symmetrical stream cipher in which the plaintext is combined with a random or pseudorandom stream of data ( the " keystream ") of the same length, to generate the ciphertext, using the Boolean " exclusive or " ( XOR ) function.

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.

Let me pass over the trip to Sante Fe with something of the same speed which made Mrs. Roebuck `` wonduh if the wahtahm speed limit '' ( 35 m.p.h. ) `` is still in ee-faket ''.

The content is not the same, however: rather than individual security, it is the security and continuing existence of an `` ideological group '' -- those in the `` free world '' -- that is basic.

The stink is all the same to me, but I really think they can make one another out blindfolded ''.

I knew that a conversation with the author would not settle such questions, because a man is not the same as his writing: in the last analysis, the questions had to be settled by the work itself.

At the same time, he is plainly sympathetic, clearly friendly.

How is the beat poet to achieve unity of form when he is at the same time engaged in a systematic derangement of senses.

Robert Penn Warren puts it this way in `` Brother To Dragons '': `` The recognition of complicity is the beginning of innocence '', where innocence, I think, means about the same thing as redemption.

One is that they were established, or gained eminence, under pressure provided by these same immigrants, from whom the old families wished to segregate their children.

At the same time, because the personal code of the detective coincides with the legal dictates of his society, because he likes to catch criminals, he is in middle class eyes a virtuous man.

The same command is repeated as many times as there are levels in rank from general to corporal.

And it is clearly argued by Lord Percy of Newcastle, in his remarkable long essay, The Heresy Of Democracy, and in a more general way by Voegelin, in his New Science Of Politics, that this same Rousseauan idea, descending through European democracy, is the source of Marx's theory of the dictatorship of the proletariat.

It is to say rather, I believe, that he has brought to bear on the history, the traditions, and the lore of his region a critical, skeptical mind -- the same mind which has made of him an inveterate experimenter in literary form and technique.

At the same time, I am aware that my recoil could be interpreted by readers of the tea leaves at the bottom of my psyche as an incestuous sign, since theirs is a science of paradox: if one hates, they say it is because one loves ; ;

This is a problem to be solved not by America alone, but also by every nation cherishing the same ideals and in position to provide help.

No matter how earnest is our quest for guaranteed peace, we must maintain a high degree of military effectiveness at the same time we are engaged in negotiating the issue of arms reduction.

It is not the same dress as the one on her manikin in the Smithsonian.

She had stood at the bottom of the stairs, as usual, when Mrs. Coolidge came down, in the same dress that is now in the Smithsonian, to greet her guests.

In this domain the simple fact of coexistence in the same local, national, and world community is enough to guarantee that we cannot refrain from having some effect, large or small, upon Gentile-Jewish relations.

The symposium provides an opportunity to confront the self with specific statements which were made at particular times by identifiable communicators who were addressing definite audiences -- and throughout several hundred pages everyone is talking about the same key symbol of identification.

It is true that this distinction between style and idea often approaches the arbitrary since in the end we must admit that style and content frequently influence or interpenetrate one another and sometimes appear as expressions of the same insight.