14.1. — Secure hashes and message digests
Source code:
This module implements a common interface to many different secure hash and message digest algorithms. Included are the FIPS secure hash algorithms SHA1, SHA224, SHA256, SHA384, and SHA512 (defined in FIPS 180-2) as well as RSA’s MD5 algorithm (defined in Internet ). The terms secure hash and message digest are interchangeable. Older algorithms were called message digests. The modern term is secure hash.
Note
If you want the adler32 or crc32 hash functions, they are available in the module.
Warning
Some algorithms have known hash collision weaknesses, refer to the “See also” section at the end.
There is one constructor method named for each type of hash. All return a hash object with the same simple interface. For example: use sha1() to create a SHA1 hash object. You can now feed this object with arbitrary strings using the update() method. At any point you can ask it for the digest of the concatenation of the strings fed to it so far using the digest() or hexdigest() methods.
Constructors for hash algorithms that are always present in this module are , sha1(), sha224(), sha256(), sha384(), and sha512(). Additional algorithms may also be available depending upon the OpenSSL library that Python uses on your platform.
For example, to obtain the digest of the string 'Nobody inspects the spammish repetition':
>>> >>> import hashlib>>> m = hashlib.md5()>>> m.update("Nobody inspects")>>> m.update(" the spammish repetition")>>> m.digest()'\xbbd\x9c\x83\xdd\x1e\xa5\xc9\xd9\xde\xc9\xa1\x8d\xf0\xff\xe9'>>> m.digest_size16>>> m.block_size64 More condensed:
>>> >>> hashlib.sha224("Nobody inspects the spammish repetition").hexdigest()'a4337bc45a8fc544c03f52dc550cd6e1e87021bc896588bd79e901e2' A generic constructor that takes the string name of the desired algorithm as its first parameter also exists to allow access to the above listed hashes as well as any other algorithms that your OpenSSL library may offer. The named constructors are much faster than and should be preferred.
Using with an algorithm provided by OpenSSL:
>>> >>> h = hashlib.new('ripemd160')>>> h.update("Nobody inspects the spammish repetition")>>> h.hexdigest()'cc4a5ce1b3df48aec5d22d1f16b894a0b894eccc' This module provides the following constant attribute:
hashlib. algorithms -
A tuple providing the names of the hash algorithms guaranteed to be supported by this module.
hashlib. algorithms_guaranteed -
A set containing the names of the hash algorithms guaranteed to be supported by this module on all platforms.
hashlib. algorithms_available -
A set containing the names of the hash algorithms that are available in the running Python interpreter. These names will be recognized when passed to . will always be a subset. The same algorithm may appear multiple times in this set under different names (thanks to OpenSSL).
The following values are provided as constant attributes of the hash objects returned by the constructors:
hash. digest_size -
The size of the resulting hash in bytes.
hash. block_size -
The internal block size of the hash algorithm in bytes.
A hash object has the following methods:
hash. update ( arg ) -
Update the hash object with the string arg. Repeated calls are equivalent to a single call with the concatenation of all the arguments: m.update(a); m.update(b) is equivalent to m.update(a+b).
Changed in version 2.7: The Python GIL is released to allow other threads to run while hash updates on data larger than 2048 bytes is taking place when using hash algorithms supplied by OpenSSL.
hash. digest ( ) -
Return the digest of the strings passed to the method so far. This is a string of bytes which may contain non-ASCII characters, including null bytes.
hash. hexdigest ( ) -
Like except the digest is returned as a string of double length, containing only hexadecimal digits. This may be used to exchange the value safely in email or other non-binary environments.
hash. copy ( ) -
Return a copy (“clone”) of the hash object. This can be used to efficiently compute the digests of strings that share a common initial substring.
14.1.1. Key derivation
Key derivation and key stretching algorithms are designed for secure password hashing. Naive algorithms such as sha1(password) are not resistant against brute-force attacks. A good password hashing function must be tunable, slow, and include a .
hashlib. pbkdf2_hmac ( name, password, salt, rounds, dklen=None ) -
The function provides PKCS#5 password-based key derivation function 2. It uses HMAC as pseudorandom function.
The string name is the desired name of the hash digest algorithm for HMAC, e.g. ‘sha1’ or ‘sha256’. password and salt are interpreted as buffers of bytes. Applications and libraries should limit password to a sensible value (e.g. 1024). salt should be about 16 or more bytes from a proper source, e.g. .
The number of rounds should be chosen based on the hash algorithm and computing power. As of 2013, at least 100,000 rounds of SHA-256 is suggested.
dklen is the length of the derived key. If dklen is None then the digest size of the hash algorithm name is used, e.g. 64 for SHA-512.
>>> >>> import hashlib, binascii>>> dk = hashlib.pbkdf2_hmac('sha256', b'password', b'salt', 100000)>>> binascii.hexlify(dk)b'0394a2ede332c9a13eb82e9b24631604c31df978b4e2f0fbd2c549944f9d79a5' Note
A fast implementation of pbkdf2_hmac is available with OpenSSL. The Python implementation uses an inline version of . It is about three times slower and doesn’t release the GIL.
See also
Module - A module to generate message authentication codes using hashes.
Module - Another way to encode binary hashes for non-binary environments.
- The FIPS 180-2 publication on Secure Hash Algorithms.
- Wikipedia article with information on which algorithms have known issues and what that means regarding their use.
import hashlibimport os,sysdef CalcSha1(filepath): with open(filepath,'rb') as f: sha1obj = hashlib.sha1() sha1obj.update(f.read()) hash = sha1obj.hexdigest() print(hash) return hashdef CalcMD5(filepath): with open(filepath,'rb') as f: md5obj = hashlib.md5() md5obj.update(f.read()) hash = md5obj.hexdigest() print(hash) return hash if __name__ == "__main__": if len(sys.argv)==2 : hashfile = sys.argv[1] if not os.path.exists(hashfile): hashfile = os.path.join(os.path.dirname(__file__),hashfile) if not os.path.exists(hashfile): print("cannot found file") else CalcMD5(hashfile) else: CalcMD5(hashfile) #raw_input("pause") else: print("no filename") 使用Python进行文件Hash计算有两点必须要注意：
1、文件打开方式一定要是二进制方式，既打开文件时使用b模式，否则Hash计算是基于文本的那将得到错误的文件Hash(网上看到有人说遇到Python的Hash计算错误在大多是由于这个原因造成的)。
2、对于MD5如果需要16位(bytes)的值那么调用对象的digest()而hexdigest(）默认是32位(bytes)，同理Sha1的digest()和hexdigest()分别产生20位(bytes)和40位(bytes)的hash值
hash ( object ) Return the hash value of the object (if it has one). Hash values are integers. They are used to quickly compare dictionary keys during a dictionary lookup. Numeric values that compare equal have the same hash value (even if they are of different types, as is the case for 1 and 1.0).
看核心编程时候有个叫hash的东西,呵呵,打开文档看看:
hashable(可哈希性) -
An object is hashable if it has a hash value which never changes during its lifetime (it needs a method), and can be compared to other objects (it needs an or method). Hashable objects which compare equal must have the same hash value.
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(如果一个对象是可哈希的,那么在它的生存期内必须不可变(需要一个哈希函数),而且可以和其他对象比较(需要比较方法).比较值相同的对象一定有相同的哈希值)
翻译的比较生硬...简单的说就是生存期内可变的对象不可以哈希,就是说改变时候其id()是不变的.基本就是说列表,字典,集合了.
写一段代码验证一下:
a= [0,0,0] b = {1:2,'c':9} c = set(a) string = 'hello' class A(): pass a = A() print hash(A) print hash(a) print hash(string) print hash(c) print hash(b) print hash(a) 可以看出列表,字典,集合是无法哈希的,因为他们在改变值的同时却没有改变id,无法由地址定位值的唯一性,因而无法哈希.