cert.py 文件源码

 复制代码def pkcs_mgf1(mgfSeed, maskLen, h):
    """
    Implements generic MGF1 Mask Generation function as described in
    Appendix B.2.1 of RFC 3447. The hash function is passed by name.
    valid values are 'md2', 'md4', 'md5', 'sha1', 'tls, 'sha256',
    'sha384' and 'sha512'. Returns None on error.

    Input:
       mgfSeed: seed from which mask is generated, an octet string
       maskLen: intended length in octets of the mask, at most 2^32 * hLen
                hLen (see below)
       h      : hash function name (in 'md2', 'md4', 'md5', 'sha1', 'tls',
                'sha256', 'sha384'). hLen denotes the length in octets of
                the hash function output.

    Output:
       an octet string of length maskLen
    """

    # steps are those of Appendix B.2.1
    if not _hashFuncParams.has_key(h):
        warning("pkcs_mgf1: invalid hash (%s) provided")
        return None
    hLen = _hashFuncParams[h][0]
    hFunc = _hashFuncParams[h][1]
    if maskLen > 2**32 * hLen:                               # 1)
        warning("pkcs_mgf1: maskLen > 2**32 * hLen")         
        return None
    T = ""                                                   # 2)
    maxCounter = math.ceil(float(maskLen) / float(hLen))     # 3)
    counter = 0
    while counter < maxCounter:
        C = pkcs_i2osp(counter, 4)
        T += hFunc(mgfSeed + C)
        counter += 1
    return T[:maskLen]