问题的解决方案是，在使用Python cryptography库和JS Forge库进行pkcs #7签名时，需要注意两个库在编码方式上的差异。具体来说，Python cryptography库默认使用DER编码格式，而JS Forge库默认使用PEM编码格式。因此，在数据传输和处理过程中，需要将数据在两种编码格式之间进行相互转换。

以下是Python cryptography库中进行pkcs #7签名的示例代码：

from cryptography.hazmat.primitives import serialization, hashes
from cryptography.hazmat.primitives.asymmetric import padding, utils

def pkcs7_sign(private_key, cert, data):
    builder = cert.signature_builder(padding.PKCS1v15(), hashes.SHA256())
    signature = private_key.sign(data, padding.PKCS1v15(), hashes.SHA256())
    signed = builder.build(signature)
    return signed

# Usage:
# private_key and cert should be loaded from file
data = b'test data'
signed_data = pkcs7_sign(private_key, cert, data)

以下是JS Forge库中进行pkcs #7签名的示例代码：

const forge = require('node-forge');

function pkcs7_sign(privateKeyPem, certPem, data) {
  const privateKey = forge.pki.privateKeyFromPem(privateKeyPem);
  const cert = forge.pki.certificateFromPem(certPem);

  const p7 = forge.pkcs7.createSignedData();
  p7.content = forge.util.createBuffer(data);
  p7.addCertificate(cert);
  p7.addSigner({
    key: privateKey,
    certificate: cert,
    digestAlgorithm: forge.pki.oids.sha256,
    authenticatedAttributes: [{
      type: forge.pki.oids.contentType,
      value: forge.pki.oids.data,
    }, {
      type: forge.pki.oids.messageDigest,
      value: forge.util.encode64(forge.md.sha256.create().update(data).digest().getBytes()),
    }, {
      type: forge.pki.oids.signingTime,
      value: new Date(),
    }],
  });
  p7.sign();

  return forge.asn1.toDer(p7.toAsn1()).getBytes();
}

// Usage:
// privateKeyPem and certPem should be loaded from file
const data = 'test data';
const signedData = pkcs7_sign(privateKeyPem, certPem, data);

在两种编码格式之间进行转换，可以使用以下代码：

from cryptography.hazmat.primitives import serialization

def der_to_pem(der_data):
    pem_data = serialization.load_der_public_key(der_data).public_bytes(
        encoding=serialization.Encoding.PEM,
        format=serialization.PublicFormat.SubjectPublicKeyInfo,
    )
    return pem_data

def pem_to_der(pem_data):
    der_data = serialization.load_pem_public_key(pem_data).public_bytes(
        encoding=serialization.Encoding.DER,
        format=serialization.PublicFormat.SubjectPublicKeyInfo,
    )
    return der_data

const forge = require('node-forge');

function derToPem(derData) {
  const pemData = forge.pki.publicKeyToPem(forge.pki.publicKeyFromAsn1(forge.asn1.fromDer(derData)));
  return pemData;
}

function pemToDer(pemData) {
  const derData = forge.asn1.toDer(forge.pki.publicKeyToAsn1(forge.pki.publicKeyFromPem(pemData))).getBytes();
  return derData;
}