Generate Digital Signature for Hash

import hashlib
import base64
import sys
import os

# ASN.1 padded bytes per hash algorithm
PADDING_BYTES = {
    'SHA1': bytes([0x30,0x21,0x30,0x09,0x06,0x05,0x2b,0x0e,0x03,0x02,0x1a,0x05,0x00,0x04]),
    'SHA256': bytes([0x30,0x31,0x30,0x0D,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x01,0x05,0x00,0x04]),
    'SHA384': bytes([0x30,0x41,0x30,0x0D,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x02,0x05,0x00,0x04]),
    'SHA512': bytes([0x30,0x51,0x30,0x0D,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x03,0x05,0x00,0x04]),
}

def compute_file_hash(filepath, algorithm):
    algo_map = {
        'SHA1': 'sha1',
        'SHA256': 'sha256',
        'SHA384': 'sha384',
        'SHA512': 'sha512',
    }
    if algorithm.upper() not in algo_map:
        raise ValueError(f"Unsupported algorithm: {algorithm}")

    hash_func = hashlib.new(algo_map[algorithm.upper()])
    with open(filepath, 'rb') as file:
        while chunk := file.read(8192):
            hash_func.update(chunk)
    return hash_func.digest()

def create_asn1_hash_encoded(hash_bytes, algorithm):
    padding = PADDING_BYTES[algorithm.upper()]
    length_byte = bytes([len(hash_bytes)])  # One byte denoting the length
    full_bytes = padding + length_byte + hash_bytes
    return base64.b64encode(full_bytes)

if __name__ == "__main__":
    if len(sys.argv) < 3:
        print("Usage: python script.py <file_path> <hash_algorithm>")
        print("Hash Algorithm: SHA1 | SHA256 | SHA384 | SHA512")
        sys.exit(1)

    file_path = sys.argv[1]
    hash_algo = sys.argv[2]

    if not os.path.isfile(file_path):
        print("Error: File not found:", file_path)
        sys.exit(1)

    try:
        hash_bytes = compute_file_hash(file_path, hash_algo)
        fileHashContent = create_asn1_hash_encoded(hash_bytes, hash_algo)
        print("fileHashContent (Base64):", fileHashContent.decode())
    except Exception as e:
        print("Error:", str(e))
        sys.exit(1)

#!/bin/bash

set -e

# Check args
if [[ $# -ne 2 ]]; then
  echo "Usage: $0 <file_path> <SHA1|SHA256|SHA384|SHA512>"
  exit 1
fi

FILE="$1"
ALG="${2^^}"

# Validate file
if [[ ! -f "$FILE" ]]; then
  echo "File not found: $FILE"
  exit 1
fi

# ASN.1 Padding Hex Map
declare -A PAD_MAP
PAD_MAP["SHA1"]="3021300906052b0e03021a050004"
PAD_MAP["SHA256"]="3031300d0609608648016503040201050004"
PAD_MAP["SHA384"]="3041300d0609608648016503040202050004"
PAD_MAP["SHA512"]="3051300d0609608648016503040203050004"

if [[ -z "${PAD_MAP[$ALG]}" ]]; then
  echo "Unsupported algorithm. Use SHA1, SHA256, SHA384, or SHA512."
  exit 1
fi

# Temp working directory
TMP_DIR=$(mktemp -d)
trap "rm -rf $TMP_DIR" EXIT

ASN1_FILE="$TMP_DIR/asn1.bin"
LEN_FILE="$TMP_DIR/len.bin"
HASH_FILE="$TMP_DIR/hash.bin"
FINAL_FILE="$TMP_DIR/final.bin"

# 1. Write ASN.1 padding to binary file
echo "${PAD_MAP[$ALG]}" | xxd -r -p > "$ASN1_FILE"

# 2. Compute hash bytes and save to file
openssl dgst "-$ALG" -binary "$FILE" > "$HASH_FILE"

# 3. Calculate hash length in bytes and write as a single byte
HASH_LEN=$(stat -c %s "$HASH_FILE")
printf "%02x\n" "$HASH_LEN" | xxd -r -p > "$LEN_FILE"

# 4. Concatenate all to final binary file
cat "$ASN1_FILE" "$LEN_FILE" "$HASH_FILE" > "$FINAL_FILE"

# 5. Base64 encode final bytes
fileHashContent=$(base64 "$FINAL_FILE")

# 6. Output
echo "fileHashContent (Base64):"
echo "$fileHashContent"

param (
    [Parameter(Mandatory=$true)][string]$FilePath,
    [Parameter(Mandatory=$true)][ValidateSet("SHA1", "SHA256", "SHA384", "SHA512")][string]$HashAlgorithm
)

# Define ASN.1 Padded Bytes for each algorithm
$paddingBytesMap = @{
    "SHA1"   = @(0x30,0x21,0x30,0x09,0x06,0x05,0x2b,0x0e,0x03,0x02,0x1a,0x05,0x00,0x04)
    "SHA256" = @(0x30,0x31,0x30,0x0D,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x01,0x05,0x00,0x04)
    "SHA384" = @(0x30,0x41,0x30,0x0D,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x02,0x05,0x00,0x04)
    "SHA512" = @(0x30,0x51,0x30,0x0D,0x06,0x09,0x60,0x86,0x48,0x01,0x65,0x03,0x04,0x02,0x03,0x05,0x00,0x04)
}

if (-not (Test-Path $FilePath)) {
    Write-Error "File not found: $FilePath"
    exit 1
}

# Compute file hash
$hashBytes = Get-FileHash -Path $FilePath -Algorithm $HashAlgorithm | Select-Object -ExpandProperty Hash
$hashBinary = [byte[]]::new($hashBytes.Length / 2)
for ($i = 0; $i -lt $hashBinary.Length; $i++) {
    $hashBinary[$i] = [Convert]::ToByte($hashBytes.Substring($i * 2, 2), 16)
}

# Get ASN.1 padding
$paddingBytes = [byte[]]$paddingBytesMap[$HashAlgorithm]

# Length byte for the hash
$lengthByte = [byte[]]@($hashBinary.Length)

# Final Byte Array = padding + lengthByte + hash
$finalBytes = $paddingBytes + $lengthByte + $hashBinary

# Base64 encode the final bytes
$fileHashContent = [Convert]::ToBase64String($finalBytes)

# Output
Write-Host "fileHashContent (Base64):"
Write-Output $fileHashContent