# can a key be applied to half the cipher text

id like to ask if we encrypt the word "hello" as "olleh" but then we apply the key to only "oll" will it be converted into its orginal form i.e "llo". this was just for example. another thing id like to as is that how much time would it take to encrypt a 1.6 mb file with an average encryption algorthm. in seconds or miliseconds. like half a second?

• Hi badaboo. You've asked two completely separate questions, which is not allowed here. The first question doesn't describe a cipher; it's simple reversal. For transposition ciphers: it depends if you can do this; if the plaintext is taken into account when encrypting you probably cannot, otherwise you can. As for the second question: that depends on the system of course: why not try yourself using openssl speed aes? My machine (a laptop with i7 low power core) manages 121 MB/s for AES-128 (which is a pretty average algorithm). – Maarten Bodewes Feb 23 '17 at 9:47
• Sheesh, wrote substitution instead of transposition. More coffee needed. – Maarten Bodewes Feb 23 '17 at 9:50

can a key be applied to half the cipher text

Stream ciphers or Block Cipher with CTR mode can do so.

how much time would it take to encrypt a 1.6 mb file with an average encryption algorthm. in seconds or miliseconds. like half a second?

It depends on hardware (CPU, speed of the driver, etc), software (OS, the programming language, etc) and the algorithm; but 1.6M Bytes should not take 0.5 seconds.

For example:

• With the AES-NI, AES(ECB) can encrypt 2G+ Bytes/s with G4500 using Java, Windows 7;
• without it, AES(ECB) encrypts around 120M Bytes/s with G2020 using Java, Windows 7.
• Twofish encrypts around 110M Bytes/s with G2020 using Java, Windows 7.
• Idea encrypts around 65M Bytes/s with G2020 using Java, Windows 7.
• does ssl support ctr mode – badaboo Feb 24 '17 at 10:36