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author | Justin Simon <jls5177@gmail.com> | 2017-05-07 04:39:47 -0500 |
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committer | Sybren A. Stüvel <sybren@stuvel.eu> | 2017-05-07 11:39:47 +0200 |
commit | 425eb24854f1c3397aaaba61fa1cf71c76b27c4b (patch) | |
tree | 824a0e34f6bc4e88bbbb6bfa7e2f7a80d5399aa3 /rsa | |
parent | 000e84a97a8ab25a5d9b4185a2e02efc033f7e8a (diff) | |
download | rsa-git-425eb24854f1c3397aaaba61fa1cf71c76b27c4b.tar.gz |
Support signing a pre-calculated hash (#87)
* Split the hashing out of the sign method
This code change adds support to split the hashing of a message
and the actual signing of the message.
* Updating unit test and documentation
This commit updates the unit test and usage docs. In addition,
This change removes a redundant error check inside rsa.sign().
* Refactore unit tests and code comments
Removed the print statements from the unit test and refactored a
few code comments to improve readability.
* Rename hash function
The new hash function had the same name as a function in the
standard library. This commit changes the name to avoid conflicts.
* Rename hash function to compute_hash()
This commit renames the hash function to compute_hash().
Diffstat (limited to 'rsa')
-rw-r--r-- | rsa/__init__.py | 5 | ||||
-rw-r--r-- | rsa/pkcs1.py | 50 |
2 files changed, 37 insertions, 18 deletions
diff --git a/rsa/__init__.py b/rsa/__init__.py index 95cd3fd..ce3a341 100644 --- a/rsa/__init__.py +++ b/rsa/__init__.py @@ -25,7 +25,7 @@ prevent repetitions, or other common security improvements. Use with care. from rsa.key import newkeys, PrivateKey, PublicKey from rsa.pkcs1 import encrypt, decrypt, sign, verify, DecryptionError, \ - VerificationError, find_signature_hash + VerificationError, find_signature_hash, sign_hash, compute_hash __author__ = "Sybren Stuvel, Barry Mead and Yesudeep Mangalapilly" __date__ = "2016-03-29" @@ -38,4 +38,5 @@ if __name__ == "__main__": doctest.testmod() __all__ = ["newkeys", "encrypt", "decrypt", "sign", "verify", 'PublicKey', - 'PrivateKey', 'DecryptionError', 'VerificationError'] + 'PrivateKey', 'DecryptionError', 'VerificationError', + 'compute_hash', 'sign_hash'] diff --git a/rsa/pkcs1.py b/rsa/pkcs1.py index 41f543c..323bf48 100644 --- a/rsa/pkcs1.py +++ b/rsa/pkcs1.py @@ -245,17 +245,16 @@ def decrypt(crypto, priv_key): return cleartext[sep_idx + 1:] -def sign(message, priv_key, hash): - """Signs the message with the private key. +def sign_hash(hash_value, priv_key, hash_method): + """Signs a precomputed hash with the private key. Hashes the message, then signs the hash with the given key. This is known as a "detached signature", because the message itself isn't altered. - - :param message: the message to sign. Can be an 8-bit string or a file-like - object. If ``message`` has a ``read()`` method, it is assumed to be a - file-like object. + + :param hash_value: A precomputed hash to sign (ignores message). Should be set to + None if needing to hash and sign message. :param priv_key: the :py:class:`rsa.PrivateKey` to sign with - :param hash: the hash method used on the message. Use 'MD5', 'SHA-1', + :param hash_method: the hash method used on the message. Use 'MD5', 'SHA-1', 'SHA-256', 'SHA-384' or 'SHA-512'. :return: a message signature block. :raise OverflowError: if the private key is too small to contain the @@ -264,15 +263,12 @@ def sign(message, priv_key, hash): """ # Get the ASN1 code for this hash method - if hash not in HASH_ASN1: - raise ValueError('Invalid hash method: %s' % hash) - asn1code = HASH_ASN1[hash] - - # Calculate the hash - hash = _hash(message, hash) + if hash_method not in HASH_ASN1: + raise ValueError('Invalid hash method: %s' % hash_method) + asn1code = HASH_ASN1[hash_method] # Encrypt the hash with the private key - cleartext = asn1code + hash + cleartext = asn1code + hash_value keylength = common.byte_size(priv_key.n) padded = _pad_for_signing(cleartext, keylength) @@ -283,6 +279,28 @@ def sign(message, priv_key, hash): return block +def sign(message, priv_key, hash_method): + """Signs the message with the private key. + + Hashes the message, then signs the hash with the given key. This is known + as a "detached signature", because the message itself isn't altered. + + :param message: the message to sign. Can be an 8-bit string or a file-like + object. If ``message`` has a ``read()`` method, it is assumed to be a + file-like object. + :param priv_key: the :py:class:`rsa.PrivateKey` to sign with + :param hash_method: the hash method used on the message. Use 'MD5', 'SHA-1', + 'SHA-256', 'SHA-384' or 'SHA-512'. + :return: a message signature block. + :raise OverflowError: if the private key is too small to contain the + requested hash. + + """ + + msg_hash = compute_hash(message, hash_method) + return sign_hash(msg_hash, priv_key, hash_method) + + def verify(message, signature, pub_key): """Verifies that the signature matches the message. @@ -305,7 +323,7 @@ def verify(message, signature, pub_key): # Get the hash method method_name = _find_method_hash(clearsig) - message_hash = _hash(message, method_name) + message_hash = compute_hash(message, method_name) # Reconstruct the expected padded hash cleartext = HASH_ASN1[method_name] + message_hash @@ -358,7 +376,7 @@ def yield_fixedblocks(infile, blocksize): break -def _hash(message, method_name): +def compute_hash(message, method_name): """Returns the message digest. :param message: the signed message. Can be an 8-bit string or a file-like |