如何解码三进制及其他非常规进制字符串？附Python脚本求助

Hey there! Let's break down what's going wrong with your current approach and walk through reliable solutions for converting non-standard bases (like base-3, base-5, etc.) to plaintext.

What's Wrong With Your Current Code? #

Your core issue is how you're mapping base-3 digits to binary: manually converting 0→00, 1→01, 2→10 creates inconsistent value translations. For example:

• Base-3 12 should equal 1*3 + 2 = 5 (binary 101), but your method turns it into 01 + 10 = 0110 (decimal 6). This off-by-one error cascades through the entire string, leading to garbage output.

Solution 1: Convert the Entire Base String to a Decimal Integer First #

This is the most universal approach for cases where the base-encoded data represents a single large integer (similar to how base64 works under the hood). Here's the fixed code:

base = 3
base_data = ""

# Read the base-3 file content
with open(f"./base{base}", "r") as b3:
    for line in b3:
        base_data += line.strip("\r\n")

# Step 1: Convert the full base-3 string to a decimal integer
decimal_num = int(base_data, base)

# Step 2: Convert the decimal integer to a byte string
# Calculate the number of bytes needed to store the integer
byte_length = (decimal_num.bit_length() + 7) // 8
# Try 'big' first; if that fails, switch to 'little' for byte order
byte_data = decimal_num.to_bytes(byte_length, byteorder="big")

# Step 3: Decode bytes to plaintext (try different encodings if utf-8 fails)
try:
    plaintext = byte_data.decode("utf-8")
except UnicodeDecodeError:
    # Fallback to replace invalid characters, or try 'ascii'/'gbk' instead
    plaintext = byte_data.decode("utf-8", errors="replace")

print(plaintext)

Solution 2: Fixed-Length Group Mapping (If Data Is Chunked) #

If the base-3 data was encoded by grouping digits to represent individual characters (like your 3-digit idea), you need to use a consistent group size that covers the full range of target characters (e.g., ASCII uses 0-127, so 6 base-3 digits work since 3^6 = 729 ≥ 128). Here's how to implement this:

base = 3
group_size = 6  # Adjust this: try 5 (3^5=243) if 6 doesn't work
base_data = ""

with open(f"./base{base}", "r") as b3:
    for line in b3:
        base_data += line.strip("\r\n")

# Pad the string with leading zeros if length isn't divisible by group size
padding = group_size - (len(base_data) % group_size)
if padding != group_size:
    base_data = "0" * padding + base_data

output = []
for i in range(0, len(base_data), group_size):
    group = base_data[i:i+group_size]
    # Convert the base-3 group to a decimal value
    decimal_val = int(group, base)
    # Map to ASCII (only if value is within valid range)
    if 0 <= decimal_val <= 127:
        output.append(chr(decimal_val))
    else:
        output.append("?")  # Replace invalid characters

print("".join(output))

Troubleshooting Tips #

• If Solution 1 gives gibberish, try switching the byteorder parameter from big to little.
• For Solution 2, test different group sizes (5, 6, 7) — check if the length of your base-3 file is evenly divisible by any of these to narrow it down.
• If decoding fails with UTF-8, try other encodings like ascii or latin-1.

内容的提问来源于stack exchange，提问作者Kennet Celeste