我正在阅读出版物FIPS 180-4 https://csrc.nist.gov/csrc/media/publications/fips/180/4/final/documents/fips180-4-draft-aug2014.pdf并尝试自己实现 SHA-256。第 15 页，标题5.3.3 SHA-256我们对初始哈希值进行了初始化：
5.3.3 SHA-256
For SHA-256, the initial hash value, H(0), shall consist of the following eight 32-bit words, in hex:
H0 = 6a09e667
H1 = bb67ae85
H2 = 3c6ef372
H3 = a54ff53a
H4 = 510e527f
H5 = 9b05688c
H6 = 1f83d9ab
H7 = 5be0cd19
These words were obtained by taking the first thirty-two bits of the fractional parts of the
square roots of the first eight prime numbers.
所以，我开始自己计算这些数字，然后我的问题出现了。根据维基百科：双精度浮点格式 https://en.wikipedia.org/wiki/Double-precision_floating-point_format以二进制表示的数字，小数部分由 0-51 位表示，指数部分由 52-62 位表示，符号部分由 63 位表示。因此，为了初始化初始哈希值，我们采用小数部分的前 32 位，即 20-51 位：
H0 = 6a09e667 (hex)
sqrt(2) = 1.4142135623730951 = [0][01111111111][01101010000010011110011001100111|11110011101111001101]
H0 = 01101010000010011110011001100111 (binary)
H0'= 01101010000010011110011001100111 (binary)
H0 == H0' -> OK
-------------------
H1 = bb67ae85 (hex)
sqrt(3) = 1.7320508075688772 = [0][01111111111][10111011011001111010111010000101|10000100110010101010]
H1 = 10111011011001111010111010000101 (binary)
H1'= 10111011011001111010111010000101 (binary)
H1 == H1' -> OK
-------------------
H2 = 3c6ef372 (hex)
sqrt(5) = 2.23606797749979 = [0][10000000000][00011110001101110111100110111001|01111111010010101000]
H2 = 00111100011011101111001101110010 (binary)
H2'= 00011110001101110111100110111001 (binary)
H2 != H2' -> SHIFTED!
-------------------
H3 = a54ff53a (hex)
sqrt(7) = 2.6457513110645907 = [0][10000000000][01010010101001111111101010011101|00101111100011101010]
H3 = 10100101010011111111010100111010 (binary)
H3'= 01010010101001111111101010011101 (binary)
H3 != H3' -> SHIFTED!
-------------------
H4 = 510e527f (hex)
sqrt(11) = 3.3166247903554 = [0][10000000000][10101000100001110010100100111111|11010110111100110100]
H4 = 01010001000011100101001001111111 (binary)
H4'= 10101000100001110010100100111111 (binary)
H4 != H4' -> SHIFTED!
-------------------
H5 = 9b05688c (hex)
sqrt(13) = 3.605551275463989 = [0][10000000000][11001101100000101011010001000110|00010101100111110011]
H5 = 10011011000001010110100010001100 (binary)
H5'= 11001101100000101011010001000110 (binary)
H5 != H5' -> SHIFTED!
-------------------
H6 = 1f83d9ab (hex)
sqrt(17) = 4.123105625617661 = [0][10000000001][00000111111000001111011001101010|11111110110100000111]
H6 = 00011111100000111101100110101011 (binary)
H6'= 00000111111000001111011001101010 (binary)
H6 != H6' -> SHIFTED!
-------------------
H7 = 5be0cd19 (hex)
sqrt(19) = 4.358898943540674 = [0][10000000001][00010110111110000011001101000110|01000100110111111001]
H7 = 01011011111000001100110100011001 (binary)
H7'= 00010110111110000011001101000110 (binary)
H7 != H7' -> SHIFTED!
-------------------
问题是为什么 H 的一些给定二进制表示FIPS 180-4 https://csrc.nist.gov/csrc/media/publications/fips/180/4/final/documents/fips180-4-draft-aug2014.pdf（似乎）以某种方式发生了变化，或者，我认为我正确地采用了小数部分，但如果没有 - 我做错了什么？
我写的代码如下：
package ru.iulgutlin.sha256;
import java.util.Arrays;
import java.util.Objects;
/**
* Test
*
* @author Rail Iulgutlin 1/9/22
*/
public class Test {
private static final long[] PRIMES = new long[64];
/**
* Given H values
*/
private static final long h0 = 0x6a09e667L;
private static final long h1 = 0xbb67ae85L;
private static final long h2 = 0x3c6ef372L;
private static final long h3 = 0xa54ff53aL;
private static final long h4 = 0x510e527fL;
private static final long h5 = 0x9b05688cL;
private static final long h6 = 0x1f83d9abL;
private static final long h7 = 0x5be0cd19L;
private static final long[] h = {h0, h1, h2, h3, h4, h5, h6, h7};
static {
initPrimes();
}
public static void main(String[] args) {
long[] s = new long[8];
for (int i = 0; i < s.length; i++) {
/**
* Calculating my own H' values and comparing with given
*/
double sqrt = Math.sqrt(PRIMES[i]);
s[i] = firstFractionalParts(sqrt, 32);
String h = binary(CustomSha256.h[i], 32); // h given binary string representation
String h_ = binary(s[i], 32); // h' calculated binary string representation
boolean eq = Objects.equals(h, h_);
// print result pretty formatted
print(" H" + i + " = " + Long.toHexString(CustomSha256.h[i]) + " (hex)");
print(" sqrt(" + PRIMES[i] + ") = " + sqrt +
" = " + new StringBuilder(binary(Double.doubleToRawLongBits(sqrt), 64))
.insert(0, '[')
.insert(2, "][")
.insert(15, "][")
.insert(49, '|')
.insert(70, ']'));
print(" H" + i + " = " + h + " (binary)");
print(" H" + i + "'= " + h_ + " (binary)");
print(" H" + i + (eq ? " == " : " != ") + "H" + i + "' -> " + (eq ? " OK " : " SHIFTED! "));
print(" -------------------");
}
}
/**
* Returns first k bits of fractional part bits of d.
* <p>
* Example calling with d = 1.7320508075688772 and k = 32:
* d = [0][01111111111][10111011011001111010111010000101|10000100110010101010]
* Returns:
* [10111011011001111010111010000101]
*
* @param d double number
* @param k number of bits
* @return first k bits of fractional part bits of d
*/
private static long firstFractionalParts(double d, int k) {
// first 12 bits are not fractional
// Example: given d = [0][01111111111][10111011011001111010111010000101][10000100110010101010] and k = 32
// first rotate bits to right so that first bit we need will stay in the rightest position
// we get [10000100110010101010][0][01111111111][10111011011001111010111010000101]
// second cut everything redundant and return
// [00000000000000000000][0][00000000000][10111011011001111010111010000101]
return cut(rotate(Double.doubleToRawLongBits(d), Double.SIZE - 12 - k), k);
}
/**
* Cuts(turns to 0) every bit of b except right k bits.
* <p>
* Example calling with b = 10111011001 = 1497 and k = 4
* Returns 00000001001 (only 4 right bits remain)
*
* @param b bits
* @param k nuber of bits to remain
* @return cutted bits
*/
private static long cut(long b, int k) {
return b & (-1L >>> (Long.SIZE - k));
}
/**
* Rotates bits right to a given k positions within 64 bits.
* Example calling with b = 0000000000000000000000000000000000000000000000000000010111011001 = 1497 and k = 3
* Returns 0010000000000000000000000000000000000000000000000000000010111011 (rotated right to 3 positions)
*
* @param bits bits to rotate
* @param k positions
* @return rotated value
*/
private static long rotate(long bits, int k) {
return ((bits >>> k) | (bits << (Long.SIZE - k)));
}
private static String binary(long b, int k) {
return String.format("%" + k + "s", Long.toBinaryString(b & (-1L >>> (Long.SIZE - k)))).replace(' ', '0');
}
private static void initPrimes() {
int i = 0;
long k = 0;
while (i < 64) {
if (isPrime(k)) {
PRIMES[i] = k;
i++;
}
k++;
}
print("PRIMES : " + Arrays.toString(PRIMES));
}
private static boolean isPrime(long a) {
if (a < 2) return false;
if (a == 2) return true;
if (a % 2 == 0) return false;
for (long i = 3; i * i <= a; i += 2)
if (a % i == 0) return false;
return true;
}
private static void print(Object o) {
System.out.println(o);
}
}
