mozilla/pdf.js · error · FormatError

Unknown crypto method

Error message

Unknown crypto method

What it means

FormatError thrown by the V=4/V=5 cipher resolver when a crypt filter's CFM (Crypt Filter Method) name is not one of the supported values: None, AESV3, V2, AESV2. An unknown CFM means pdf.js has no cipher implementation for that filter and cannot decrypt streams referencing it.

Source

Thrown at src/core/crypto.js:1329

              num,
              gen,
              this.encryptionKey,
              /* isAes = */ false
            )
          );
        }
        if (cfm.name === "AESV2") {
          return AES128Cipher.bind(
            null,
            this.#buildObjectKey(
              num,
              gen,
              this.encryptionKey,
              /* isAes = */ true
            )
          );
        }
        throw new FormatError("Unknown crypto method");
      };

      const transform = new CipherTransform(
        resolveCipher,
        this.strf,
        this.stmf
      );
      transform.embeddedFilterName = this.eff;
      return transform;
    }

    // algorithms 1 and 2
    /** @type {ResolveCipher} */
    const resolveCipher = () =>
      ARCFourCipher.bind(
        null,
        this.#buildObjectKey(num, gen, this.encryptionKey, /* isAes = */ false)
      );

View on GitHub (pinned to 5903d58d58)

Solutions

1. Re-encrypt with a supported CFM (V2 RC4, AESV2, AESV3).
2. If only some streams use the unsupported filter, set those CF entries to None or remap them to Identity to skip decryption (advanced, may yield unreadable content).
3. Surface an 'unsupported crypt filter method' message.

try {
  const doc = await getDocument({ url }).promise;
} catch (e) {
  if (e.name === 'FormatError' && e.message === 'Unknown crypto method') {
    notifyUser('Unsupported crypt filter method (CFM). Only None, V2, AESV2, AESV3 are supported.');
    return;
  }
  throw e;
}

When it happens

Trigger: A CF dict entry with CFM set to a future or proprietary method (e.g., AESV4); a corrupt CFM value; a producer that emits a custom crypt filter method.

Common situations: Newer encryption methods pdf.js has not adopted; hand-edited CF dicts; buggy producers.

Related errors

• unknown encryption method
• unsupported encryption algorithm
• Invalid crypt filter name.
• invalid key length
• No password given

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/2d8530b068556493. Report an issue: GitHub.