SHA-256 Merkle tree: Difference between revisions
m (Minor edit to Java code) |
m (Minor edit to C++ code) |
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Line 126:
void print_digest(std::ostream& out, const std::vector<unsigned char>& digest) {
out << std::hex << std::setfill('0');
for (size_t i = 0; i < digest.size(); ++i)
out << std::setw(2
out << '\n';
}
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Revision as of 11:41, 11 December 2020
You are encouraged to solve this task according to the task description, using any language you may know.
As described in its documentation, Amazon S3 Glacier requires that all uploaded files come with a checksum computed as a Merkle Tree using SHA-256.
Specifically, the SHA-256 hash is computed for each 1MiB block of the file. And then, starting from the beginning of the file, the raw hashes of consecutive blocks are paired up and concatenated together, and a new hash is computed from each concatenation. Then these are paired up and concatenated and hashed, and the process continues until there is only one hash left, which is the final checksum. The hexadecimal representation of this checksum is the value that must be included with the AWS API call to upload the object (or complete a multipart upload).
Implement this algorithm in your language; you can use the code from the SHA-256 task for the actual hash computations. For better manageability and portability, build the tree using a smaller block size of only 1024 bytes, and demonstrate it on the RosettaCode title image with that block size. The final result should be the hexadecimal digest value a4f902cf9d51fe51eda156a6792e1445dff65edf3a217a1f3334cc9cf1495c2c.
C
<lang c>#include <glib.h>
- include <stdlib.h>
- include <stdio.h>
- include <string.h>
guchar* sha256_merkle_tree(FILE* in, size_t block_size) {
gchar* buffer = g_malloc(block_size); GPtrArray* hashes = g_ptr_array_new_with_free_func(g_free); gssize digest_length = g_checksum_type_get_length(G_CHECKSUM_SHA256); GChecksum* checksum = g_checksum_new(G_CHECKSUM_SHA256); size_t bytes; while ((bytes = fread(buffer, 1, block_size, in)) > 0) { g_checksum_reset(checksum); g_checksum_update(checksum, (guchar*)buffer, bytes); gsize len = digest_length; guchar* digest = g_malloc(len); g_checksum_get_digest(checksum, digest, &len); g_ptr_array_add(hashes, digest); } g_free(buffer); guint hashes_length = hashes->len; if (hashes_length == 0) { g_ptr_array_free(hashes, TRUE); g_checksum_free(checksum); return NULL; } while (hashes_length > 1) { guint j = 0; for (guint i = 0; i < hashes_length; i += 2, ++j) { guchar* digest1 = g_ptr_array_index(hashes, i); guchar* digest_out = g_ptr_array_index(hashes, j); if (i + 1 < hashes_length) { guchar* digest2 = g_ptr_array_index(hashes, i + 1); g_checksum_reset(checksum); g_checksum_update(checksum, digest1, digest_length); g_checksum_update(checksum, digest2, digest_length); gsize len = digest_length; g_checksum_get_digest(checksum, digest_out, &len); } else { memcpy(digest_out, digest1, digest_length); } } hashes_length = j; } guchar* result = g_ptr_array_steal_index(hashes, 0); g_ptr_array_free(hashes, TRUE); g_checksum_free(checksum); return result;
}
int main(int argc, char** argv) {
if (argc != 2) { fprintf(stderr, "usage: %s filename\n", argv[0]); return EXIT_FAILURE; } FILE* in = fopen(argv[1], "rb"); if (in) { guchar* digest = sha256_merkle_tree(in, 1024); fclose(in); if (digest) { gssize length = g_checksum_type_get_length(G_CHECKSUM_SHA256); for (gssize i = 0; i < length; ++i) printf("%02x", digest[i]); printf("\n"); g_free(digest); } } else { perror(argv[1]); return EXIT_FAILURE; } return EXIT_SUCCESS;
}</lang>
- Output:
a4f902cf9d51fe51eda156a6792e1445dff65edf3a217a1f3334cc9cf1495c2c
C++
<lang cpp>#include <cstdlib>
- include <fstream>
- include <iomanip>
- include <iostream>
- include <vector>
- include <openssl/sha.h>
class sha256_exception : public std::exception { public:
const char* what() const noexcept override { return "SHA-256 error"; }
};
class sha256 { public:
sha256() { reset(); } sha256(const sha256&) = delete; sha256& operator=(const sha256&) = delete; void reset() { if (SHA256_Init(&context_) == 0) throw sha256_exception(); } void update(const void* data, size_t length) { if (SHA256_Update(&context_, data, length) == 0) throw sha256_exception(); } std::vector<unsigned char> digest() { std::vector<unsigned char> digest(SHA256_DIGEST_LENGTH); if (SHA256_Final(digest.data(), &context_) == 0) throw sha256_exception(); return digest; }
private:
SHA256_CTX context_;
};
void print_digest(std::ostream& out, const std::vector<unsigned char>& digest) {
out << std::hex << std::setfill('0'); for (size_t i = 0; i < digest.size(); ++i) out << std::setw(2) << static_cast<int>(digest[i]); out << '\n';
}
std::vector<unsigned char> sha256_merkle_tree(std::istream& in, size_t block_size) {
std::vector<std::vector<unsigned char>> hashes; std::vector<char> buffer(block_size); sha256 md; while (in) { in.read(buffer.data(), block_size); size_t bytes = in.gcount(); if (bytes == 0) break; md.reset(); md.update(buffer.data(), bytes); hashes.push_back(md.digest()); } if (hashes.empty()) return {}; size_t length = hashes.size(); while (length > 1) { size_t j = 0; for (size_t i = 0; i < length; i += 2, ++j) { auto& digest1 = hashes[i]; auto& digest_out = hashes[j]; if (i + 1 < length) { auto& digest2 = hashes[i + 1]; md.reset(); md.update(digest1.data(), digest1.size()); md.update(digest2.data(), digest2.size()); digest_out = md.digest(); } else { digest_out = digest1; } } length = j; } return hashes[0];
}
int main(int argc, char** argv) {
if (argc != 2) { std::cerr << "usage: " << argv[0] << " filename\n"; return EXIT_FAILURE; } std::ifstream in(argv[1], std::ios::binary); if (!in) { std::cerr << "Cannot open file " << argv[1] << ".\n"; return EXIT_FAILURE; } try { print_digest(std::cout, sha256_merkle_tree(in, 1024)); } catch (const std::exception& ex) { std::cerr << ex.what() << "\n"; return EXIT_FAILURE; } return EXIT_SUCCESS;
}</lang>
- Output:
a4f902cf9d51fe51eda156a6792e1445dff65edf3a217a1f3334cc9cf1495c2c
Factor
<lang factor>USING: checksums checksums.sha fry grouping io io.encodings.binary io.files kernel make math math.parser namespaces sequences ;
- each-block ( ... size quot: ( ... block -- ... ) -- ... )
input-stream get spin (each-stream-block) ; inline
- >sha-256 ( seq -- newseq ) sha-256 checksum-bytes ;
- (hash-read) ( path encoding chunk-size -- )
'[ _ [ >sha-256 , ] each-block ] with-file-reader ;
! Read a file in chunks as a sequence of sha-256 hashes, so as ! not to store a potentially large file in memory all at once.
- hash-read ( path chunk-size -- seq )
binary swap [ (hash-read) ] { } make ;
- hash-combine ( seq -- newseq )
2 <groups> [ dup length 1 > [ concat >sha-256 ] [ first ] if ] map ;
- merkle-hash ( path chunk-size -- str )
hash-read [ dup length 1 = ] [ hash-combine ] until first bytes>hex-string ;
"title.png" 1024 merkle-hash print</lang>
- Output:
a4f902cf9d51fe51eda156a6792e1445dff65edf3a217a1f3334cc9cf1495c2c
Go
<lang go>package main
import (
"crypto/sha256" "fmt" "io" "log" "os"
)
func main() {
const blockSize = 1024 f, err := os.Open("title.png") if err != nil { log.Fatal(err) } defer f.Close()
var hashes [][]byte buffer := make([]byte, blockSize) h := sha256.New() for { bytesRead, err := f.Read(buffer) if err != nil { if err != io.EOF { log.Fatal(err) } break } h.Reset() h.Write(buffer[:bytesRead]) hashes = append(hashes, h.Sum(nil)) } buffer = make([]byte, 64) for len(hashes) > 1 { var hashes2 [][]byte for i := 0; i < len(hashes); i += 2 { if i < len(hashes)-1 { copy(buffer, hashes[i]) copy(buffer[32:], hashes[i+1]) h.Reset() h.Write(buffer) hashes2 = append(hashes2, h.Sum(nil)) } else { hashes2 = append(hashes2, hashes[i]) } } hashes = hashes2 } fmt.Printf("%x", hashes[0]) fmt.Println()
}</lang>
- Output:
a4f902cf9d51fe51eda156a6792e1445dff65edf3a217a1f3334cc9cf1495c2c
Java
<lang java>import java.io.*; import java.security.*; import java.util.*;
public class SHA256MerkleTree {
public static void main(String[] args) { try { if (args.length != 1) { System.err.println("missing file argument"); System.exit(1); } try (InputStream in = new BufferedInputStream(new FileInputStream(args[0]))) { byte[] digest = sha256MerkleTree(in, 1024); if (digest != null) System.out.println(digestToString(digest)); } } catch (Exception e) { e.printStackTrace(); } }
private static String digestToString(byte[] digest) { StringBuilder result = new StringBuilder(); for (int i = 0; i < digest.length; ++i) result.append(String.format("%02x", digest[i])); return result.toString(); }
private static byte[] sha256MerkleTree(InputStream in, int blockSize) throws Exception { byte[] buffer = new byte[blockSize]; int bytes; MessageDigest md = MessageDigest.getInstance("SHA-256"); List<byte[]> digests = new ArrayList<>(); while ((bytes = in.read(buffer)) > 0) { md.reset(); md.update(buffer, 0, bytes); digests.add(md.digest()); } int length = digests.size(); if (length == 0) return null; while (length > 1) { int j = 0; for (int i = 0; i < length; i += 2, ++j) { byte[] digest1 = digests.get(i); if (i + 1 < length) { byte[] digest2 = digests.get(i + 1); md.reset(); md.update(digest1); md.update(digest2); digests.set(j, md.digest()); } else { digests.set(j, digest1); } } length = j; } return digests.get(0); }
}</lang>
- Output:
a4f902cf9d51fe51eda156a6792e1445dff65edf3a217a1f3334cc9cf1495c2c
Julia
<lang julia>using SHA
function merkletree(filename="title.png", blocksize=1024)
bytes = codeunits(read(filename, String)) len = length(bytes) hsh = [sha256(view(bytes. i:min(i+blocksize-1, len)])) for i in 1:1024:len] len = length(hsh) while len > 1 hsh = [i == len ? hsh[i] : sha256(vcat(hsh[i], hsh[i + 1])) for i in 1:2:len] len = length(hsh) end return bytes2hex(hsh[1])
end
println(merkletree())
</lang>
- Output:
a4f902cf9d51fe51eda156a6792e1445dff65edf3a217a1f3334cc9cf1495c2c
Phix
<lang Phix>include builtins\libcurl.e include builtins\sha256.e
constant ONE_MB = 1024 * 1024
function merkle(string filename, url, integer block_size=ONE_MB)
if not file_exists(filename) then printf(1,"Downloading %s...\n",{filename}) CURLcode res = curl_easy_get_file(url,"",filename) -- (no proxy) if res!=CURLE_OK then string error = sprintf("%d",res) if res=CURLE_COULDNT_RESOLVE_HOST then error &= " [CURLE_COULDNT_RESOLVE_HOST]" end if crash("Error %s downloading file\n", {error}) end if end if string data = get_text(filename) sequence blocks = {} for i=1 to length(data) by block_size do blocks = append(blocks,sha256(data[i..min(i+block_size-1,length(data))])) end for while length(blocks)>1 do integer l = 0 for i=1 to length(blocks) by 2 do l += 1 blocks[l] = iff(i<length(blocks)?sha256(blocks[i]&blocks[i+1]) :blocks[i]) end for blocks = blocks[1..l] end while return blocks[1]
end function
function asHex(string s) string res = ""
for i=1 to length(s) do res &= sprintf("%02X",s[i]) end for return res
end function
printf(1,"%s\n",asHex(merkle("title.png", "https://rosettacode.org/mw/title.png", 1024)))</lang>
- Output:
a4f902cf9d51fe51eda156a6792e1445dff65edf3a217a1f3334cc9cf1495c2c
Python
This version attempts to combine blocks as soon as possible to minimize the memory footprint.
<lang Python>#!/usr/bin/env python
- compute the root label for a SHA256 Merkle tree built on blocks of a given
- size (default 1MB) taken from the given file(s)
import argh import hashlib import sys
@argh.arg('filename', nargs='?', default=None) def main(filename, block_size=1024*1024):
if filename: fin = open(filename, 'rb') else: fin = sys.stdin stack = [] block = fin.read(block_size) while block: # a node is a pair: ( tree-level, hash ) node = (0, hashlib.sha256(block).digest()) stack.append(node)
# concatenate adjacent pairs at the same level while len(stack) >= 2 and stack[-2][0] == stack[-1][0]: a = stack[-2] b = stack[-1] l = a[0] stack[-2:] = [(l+1, hashlib.sha256(a[1] + b[1]).digest())]
block = fin.read(block_size) while len(stack) > 1: # at the end we have to concatenate even across levels a = stack[-2] b = stack[-1] al = a[0] bl = b[0] stack[-2:] = [(max(al, bl)+1, hashlib.sha256(a[1] + b[1]).digest())]
print(stack[0][1].hex())
argh.dispatch_command(main)
</lang>
- Output:
$ sha256tree.py --block-size=1024 title.png a4f902cf9d51fe51eda156a6792e1445dff65edf3a217a1f3334cc9cf1495c2c
Raku
<lang perl6>use Digest::SHA256::Native;
unit sub MAIN(Int :b(:$block-size) = 1024 × 1024, *@args);
my $in = @args ?? IO::CatHandle.new(@args) !! $*IN;
my @blocks = do while my $block = $in.read: $block-size { sha256 $block };
while @blocks > 1 {
@blocks = @blocks.batch(2).map: { $_ > 1 ?? sha256([~] $_) !! .[0] }
}
say @blocks[0]».fmt('%02x').join;</lang>
- Output:
$ sha256tree --block-size=1024 title.png a4f902cf9d51fe51eda156a6792e1445dff65edf3a217a1f3334cc9cf1495c2c