In my RSA algorithm implementation I should evaluate the following expression:
b = ((m-da)*H)mod(p-1)
While all the elements in the expression are integers, m is a String. That is a problem for me. How can I use a String in the case? Particularly I need that to sign the message m.
How can I use a String in the case?
You can't. m needs to be an integer. You need to devise some kind of encoding like convert to a byte array using some kind of character encoding like UTF-8. Then you can use some kind of encoding to unserialize the byte array into an integer. Have a look at how big-endian or little-endian type of integer encodings work.
Related
a question:
A parcel service provider requests that the password is encoded in a specific way:
KEY -> UTF8 Encoding -> SHA512
They KEY should be in byte form, not string
currently I have this in Node.js with CryptoJS:
password = CryptoJS.SHA512(CryptoJS.enc.Utf8.parse(key))
or
password = CryptoJS.SHA512(CryptoJS.enc.Utf8.stringify(key))
Don't know which one is the right one.
I need to convert the key to bytes, how do I do that?
Keys are arbitrary sequences of bytes, and SHA-512 works on arbitrary sequences of bytes. However, UTF-8 can't encode arbitrary sequences of bytes. It can only encode Unicode code points. What you're asking for isn't possible. (I suggest posting precisely what the requirement is. It's possible you're misreading it.)
You need another encoding, such as Base64 or Hex. The output of either of those is compatible with UTF-8 (they both output subsets of UTF-8).
That said, this is a very strange request, since you already have exactly the correct input for SHA-512. Converting it to a string and then converting that string back to (likely different) bytes seems a pointless step, but if you need it, you'll need a byte encoding like Base64 or Hex.
There is big hex value:
var Hex = "ad6eb61316ff805e9c94667ab04aa45aa3203eef71ba8c12afb353a5c7f11657e43f5ce4483d4e6eca46af6b3bde4981499014730d3b233420bf3ecd3287a2768da8bd401f0abd7a5a137d700f0c9d0574ef7ba91328e9a6b055820d03c98d56943139075d";
How can I convert it to big integer in node.js? I tried to search, but what I found is
var integer = parseInt(Hex, 16);
But It doesn't work if I put big hex value. I think.
the result is,
1.1564501846672726e+243
How can I return normal big integer? I want to use this value for modulus in RSA encryption. Actually I don't know I have to convert it or not.
You need precise integers to do modular arithmetic for RSA, but the largest integer in JavaScript is 9007199254740991 without losing precision. You cannot represent a larger integer as a Number. You would need to devise a way to do modular arithmetic with many chunks of the large integer or simply use one of the available like the big number arithmetic in JSBN which also provides a full implementation of RSA including PKCS#1 v1.5 padding.
Maybe a stupid question, but if I have some arbitrary binary data, can I cast it to string and back to byte array without corrupting it?
Is []byte(string(byte_array)) always the same as byte_array?
The expression []byte(string(byte_slice)) evaluates to a slice with the same length and contents as byte_slice. The capacity of the two slices may be different.
Although some language features assume that strings contain valid UTF-8 encoded text, a string can contain arbitrary bytes.
As known, Base-64 encodes binary data into transferable ASCII strings, and we decode these strings back to data.
Now my question is inverted: Can every random string be decoded as binary data, and correctly encoded back to the exact original string?
It depends upon your coding method - some methods use only a limited range of characters so a string containing other characters would not be legal. In Base64 this is the case so the answer is no. With other methods I'm sure its possible but I cannot think of an example other than simply treating the string as binary bytes.
I was reading redis manifesto[1] and it seems redis accepts only binary safe strings as keys but I don't know the difference between the two. Can anyone explain with an example?
[1] http://oldblog.antirez.com/post/redis-manifesto.html
According to Redis documentation, simple Redis strings have syntax "+redis_response\r\n" whereas bulk Redis strings have syntax "$str_len\r\nbinary_safe_string\r\n".
In other words, binary safe string in Redis can contain any data as simple as "foo" to any binary data upto 512MB say a JEPG image. Binary safe string has its length encoded in it and does not terminate with any particular character such as a NULL terminating string in C which ends with '\0.
HTH,
Swanand
I'm not familiar with the system in question, but the term "binary safe string" might be used either to describe certain string-storage types or to describe particular string instances. In a binary-safe string type, a string of length N may be used to encapsulate any sequence of N values in the range either 0-255 or 0-65535 (for 8- or 16-bit types, respectively). A binary-safe string instance might be one whose representation may be subdivided into uniformly-sized pieces, with each piece representing one character, as distinct from a string instance in which different characters require different amounts of storage space.
Some string types (which are not binary safe) will use variable-length representations for certain characters, and will behave oddly if asked to act upon e.g. a string which contains the code for "first half of a multi-part character" followed by something other than a "second half of multi-part character". Further, some code which works with strings will assume that it the Nth character will be stored in either the Nth byte or the Nth pair of bytes, and will malfunction if given a string in which, e.g. the 8th character is stored in the 12th and 13th pairs of bytes.
Looking only briefly at the link provided, I would guess that it's saying that the redis does not expect to only work with strings that use different numbers of bytes to hold different characters, though I'm not quite clear whether it's assuming that a string type will be able to handle any possible sequence of bytes, or whether it's assuming that any string instance which it's given may be safely regarded as a sequence of bytes. I think the fundamental concepts of interest, though, are (1) some string types use variable-length encodings and others do not; (2) even in types that use variable-length encodings, a useful subset of string instances will consist only of fixed-length characters.
Binary-safe means that a string can contain any character, while binary-unsafe can not, such as '\0' in C language. '\0' is the ending of a string, which means characters after '\0' and before '\0' will be considered as two different strings.