TheAlgorithms/Java · error · IllegalArgumentException

DES key must be supplied as a 64 character binary string

Error message

DES key must be supplied as a 64 character binary string

What it means

Thrown by the DES constructor (via sanitize) when the supplied key is not exactly 64 characters long. This DES implementation represents the 64-bit key as a binary string of 64 '0'/'1' characters; only the length is checked here — non-binary contents would fail later during subkey generation.

Source

Thrown at src/main/java/com/thealgorithms/ciphers/DES.java:16

package com.thealgorithms.ciphers;

/**
 * This class is build to demonstrate the application of the DES-algorithm
 * (https://en.wikipedia.org/wiki/Data_Encryption_Standard) on a plain English message. The supplied
 * key must be in form of a 64 bit binary String.
 */
public class DES {

    private String key;
    private final String[] subKeys;

    private void sanitize(String key) {
        int length = key.length();
        if (length != 64) {
            throw new IllegalArgumentException("DES key must be supplied as a 64 character binary string");
        }
    }

    DES(String key) {
        sanitize(key);
        this.key = key;
        subKeys = getSubkeys(key);
    }

    public String getKey() {
        return this.key;
    }

    public void setKey(String key) {
        sanitize(key);
        this.key = key;
    }

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Supply a 64-character string consisting only of '0' and '1'.
2. Convert an existing byte/hex key to its 64-bit binary-string representation before constructing DES.
3. Validate length == 64 and contents match [01]{64} before instantiation.

Example fix

// before
DES des = new DES(myHexKey); // e.g. "1A2B3C..."

// after
String binaryKey = padTo64(Long.toBinaryString(parseHex(myHexKey)));
if (!binaryKey.matches("[01]{64}")) throw new IllegalArgumentException("bad key");
DES des = new DES(binaryKey);

if (key == null || key.length() != 64 || !key.matches("[01]{64}")) {
    throw new IllegalArgumentException("DES key must be a 64-char binary string");
}
DES des = new DES(key);

static boolean isDesBitString(String s) { return s != null && s.matches("[01]{64}"); }

try {
    DES des = new DES(key);
} catch (IllegalArgumentException e) {
    // wrong key format; convert hex/bytes to a 64-char binary string first
}

When it happens

Trigger: Passing a hex key string (16 chars), a raw 8-byte key, a Base64 key, or a binary string of any length other than 64.

Common situations: Confusing this library's bit-string format with conventional hex/byte key formats; truncating or padding a key; using a key from another DES library that uses bytes.

Related errors

• Encrypted message should be a multiple of 64 characters in l
• Invalid Baconian code: {}
• Base, secret, and prime must be non-null and positive values
• Other public value must be non-null and positive.
• Bit length must be at least {} for security.

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/2bfcc85564ac6f8f. Report an issue: GitHub.