8. Reference¶
This is the class and function reference. For more usage information see the Usage page.
8.1. Functions¶

rsa.
encrypt
(message, pub_key)¶ Encrypts the given message using PKCS#1 v1.5
Parameters:  message – the message to encrypt. Must be a byte string no longer than
k11
bytes, wherek
is the number of bytes needed to encode then
component of the public key.  pub_key – the
rsa.PublicKey
to encrypt with.
Raises: OverflowError – when the message is too large to fit in the padded block.
>>> from rsa import key, common >>> (pub_key, priv_key) = key.newkeys(256) >>> message = b'hello' >>> crypto = encrypt(message, pub_key)
The crypto text should be just as long as the public key ‘n’ component:
>>> len(crypto) == common.byte_size(pub_key.n) True
 message – the message to encrypt. Must be a byte string no longer than

rsa.
decrypt
(crypto, priv_key)¶ Decrypts the given message using PKCS#1 v1.5
The decryption is considered ‘failed’ when the resulting cleartext doesn’t start with the bytes 00 02, or when the 00 byte between the padding and the message cannot be found.
Parameters:  crypto – the crypto text as returned by
rsa.encrypt()
 priv_key – the
rsa.PrivateKey
to decrypt with.
Raises: DecryptionError – when the decryption fails. No details are given as to why the code thinks the decryption fails, as this would leak information about the private key.
>>> import rsa >>> (pub_key, priv_key) = rsa.newkeys(256)
It works with strings:
>>> crypto = encrypt(b'hello', pub_key) >>> decrypt(crypto, priv_key) b'hello'
And with binary data:
>>> crypto = encrypt(b'\x00\x00\x00\x00\x01', pub_key) >>> decrypt(crypto, priv_key) b'\x00\x00\x00\x00\x01'
Altering the encrypted information will likely cause a
rsa.pkcs1.DecryptionError
. If you want to be sure, usersa.sign()
.Warning
Never display the stack trace of a
rsa.pkcs1.DecryptionError
exception. It shows where in the code the exception occurred, and thus leaks information about the key. It’s only a tiny bit of information, but every bit makes cracking the keys easier.>>> crypto = encrypt(b'hello', pub_key) >>> crypto = crypto[0:5] + b'X' + crypto[6:] # change a byte >>> decrypt(crypto, priv_key) Traceback (most recent call last): ... rsa.pkcs1.DecryptionError: Decryption failed
 crypto – the crypto text as returned by

rsa.
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.
Parameters:  message – the message to sign. Can be an 8bit string or a filelike
object. If
message
has aread()
method, it is assumed to be a filelike object.  priv_key – the
rsa.PrivateKey
to sign with  hash_method – the hash method used on the message. Use ‘MD5’, ‘SHA1’, ‘SHA224’, SHA256’, ‘SHA384’ or ‘SHA512’.
Returns: a message signature block.
Raises: OverflowError – if the private key is too small to contain the requested hash.
 message – the message to sign. Can be an 8bit string or a filelike
object. If

rsa.
verify
(message, signature, pub_key)¶ Verifies that the signature matches the message.
The hash method is detected automatically from the signature.
Parameters:  message – the signed message. Can be an 8bit string or a filelike
object. If
message
has aread()
method, it is assumed to be a filelike object.  signature – the signature block, as created with
rsa.sign()
.  pub_key – the
rsa.PublicKey
of the person signing the message.
Raises: VerificationError – when the signature doesn’t match the message.
Returns: the name of the used hash.
 message – the signed message. Can be an 8bit string or a filelike
object. If

rsa.
find_signature_hash
(signature, pub_key)¶ Returns the hash name detected from the signature.
If you also want to verify the message, use
rsa.verify()
instead. It also returns the name of the used hash.Parameters:  signature – the signature block, as created with
rsa.sign()
.  pub_key – the
rsa.PublicKey
of the person signing the message.
Returns: the name of the used hash.
 signature – the signature block, as created with

rsa.
newkeys
(keysize)¶ Generates public and private keys, and returns them as (pub, priv).
The public key is also known as the ‘encryption key’, and is a
rsa.PublicKey
object. The private key is also known as the ‘decryption key’ and is arsa.PrivateKey
object.Parameters:  nbits – the number of bits required to store
n = p*q
.  accurate – when True,
n
will have exactly the number of bits you asked for. However, this makes key generation much slower. When False, n` may have slightly less bits.  poolsize – the number of processes to use to generate the prime numbers. If set to a number > 1, a parallel algorithm will be used. This requires Python 2.6 or newer.
 exponent (int) – the exponent for the key; only change this if you know what you’re doing, as the exponent influences how difficult your private key can be cracked. A very common choice for e is 65537.
Returns: a tuple (
rsa.PublicKey
,rsa.PrivateKey
)The
poolsize
parameter was added in PythonRSA 3.1 and requires Python 2.6 or newer. nbits – the number of bits required to store
8.2. Classes¶
Note
Storing public and private keys via the pickle module is possible. However, it is insecure to load a key from an untrusted source. The pickle module is not secure against erroneous or maliciously constructed data. Never unpickle data received from an untrusted or unauthenticated source.

class
rsa.
PublicKey
(n, e)¶ Represents a public RSA key.
This key is also known as the ‘encryption key’. It contains the ‘n’ and ‘e’ values.
Supports attributes as well as dictionarylike access. Attribute access is faster, though.
>>> PublicKey(5, 3) PublicKey(5, 3)
>>> key = PublicKey(5, 3) >>> key.n 5 >>> key['n'] 5 >>> key.e 3 >>> key['e'] 3

blind
(message, r)¶ Performs blinding on the message using random number ‘r’.
Parameters:  message (int) – the message, as integer, to blind.
 r (int) – the random number to blind with.
Returns: the blinded message.
Return type: int
The blinding is such that message = unblind(decrypt(blind(encrypt(message))).
See https://en.wikipedia.org/wiki/Blinding_%28cryptography%29

classmethod
load_pkcs1
(keyfile, format='PEM')¶ Loads a key in PKCS#1 DER or PEM format.
Parameters:  keyfile (bytes) – contents of a DER or PEMencoded file that contains the key.
 format (str) – the format of the file to load; ‘PEM’ or ‘DER’
Returns: the loaded key
Return type: AbstractKey

classmethod
load_pkcs1_openssl_der
(keyfile)¶ Loads a PKCS#1 DERencoded public key file from OpenSSL.
Parameters: keyfile – contents of a DERencoded file that contains the public key, from OpenSSL. Returns: a PublicKey object Return type: bytes

classmethod
load_pkcs1_openssl_pem
(keyfile)¶ Loads a PKCS#1.5 PEMencoded public key file from OpenSSL.
These files can be recognised in that they start with BEGIN PUBLIC KEY rather than BEGIN RSA PUBLIC KEY.
The contents of the file before the “—–BEGIN PUBLIC KEY—–” and after the “—–END PUBLIC KEY—–” lines is ignored.
Parameters: keyfile (bytes) – contents of a PEMencoded file that contains the public key, from OpenSSL. Returns: a PublicKey object

save_pkcs1
(format='PEM')¶ Saves the key in PKCS#1 DER or PEM format.
Parameters: format (str) – the format to save; ‘PEM’ or ‘DER’ Returns: the DER or PEMencoded key. Return type: bytes

unblind
(blinded, r)¶ Performs blinding on the message using random number ‘r’.
Parameters:  blinded – the blinded message, as integer, to unblind.
 r – the random number to unblind with.
Returns: the original message.
The blinding is such that message = unblind(decrypt(blind(encrypt(message))).
See https://en.wikipedia.org/wiki/Blinding_%28cryptography%29


class
rsa.
PrivateKey
(n, e, d, p, q)¶ Represents a private RSA key.
This key is also known as the ‘decryption key’. It contains the ‘n’, ‘e’, ‘d’, ‘p’, ‘q’ and other values.
Supports attributes as well as dictionarylike access. Attribute access is faster, though.
>>> PrivateKey(3247, 65537, 833, 191, 17) PrivateKey(3247, 65537, 833, 191, 17)
exp1, exp2 and coef will be calculated:
>>> pk = PrivateKey(3727264081, 65537, 3349121513, 65063, 57287) >>> pk.exp1 55063 >>> pk.exp2 10095 >>> pk.coef 50797

blind
(message, r)¶ Performs blinding on the message using random number ‘r’.
Parameters:  message (int) – the message, as integer, to blind.
 r (int) – the random number to blind with.
Returns: the blinded message.
Return type: int
The blinding is such that message = unblind(decrypt(blind(encrypt(message))).
See https://en.wikipedia.org/wiki/Blinding_%28cryptography%29

blinded_decrypt
(encrypted)¶ Decrypts the message using blinding to prevent sidechannel attacks.
Parameters: encrypted (int) – the encrypted message Returns: the decrypted message Return type: int

blinded_encrypt
(message)¶ Encrypts the message using blinding to prevent sidechannel attacks.
Parameters: message (int) – the message to encrypt Returns: the encrypted message Return type: int

classmethod
load_pkcs1
(keyfile, format='PEM')¶ Loads a key in PKCS#1 DER or PEM format.
Parameters:  keyfile (bytes) – contents of a DER or PEMencoded file that contains the key.
 format (str) – the format of the file to load; ‘PEM’ or ‘DER’
Returns: the loaded key
Return type: AbstractKey

save_pkcs1
(format='PEM')¶ Saves the key in PKCS#1 DER or PEM format.
Parameters: format (str) – the format to save; ‘PEM’ or ‘DER’ Returns: the DER or PEMencoded key. Return type: bytes

unblind
(blinded, r)¶ Performs blinding on the message using random number ‘r’.
Parameters:  blinded – the blinded message, as integer, to unblind.
 r – the random number to unblind with.
Returns: the original message.
The blinding is such that message = unblind(decrypt(blind(encrypt(message))).
See https://en.wikipedia.org/wiki/Blinding_%28cryptography%29

8.3. Exceptions¶

class
rsa.pkcs1.
CryptoError
(Exception)¶ Base class for all exceptions in this module.

class
rsa.pkcs1.
DecryptionError
(CryptoError)¶ Raised when decryption fails.

class
rsa.pkcs1.
VerificationError
(CryptoError)¶ Raised when verification fails.
8.3.1. The VARBLOCK file format¶
Warning
The VARBLOCK format is NOT recommended for general use, has been deprecated since PythonRSA 3.4, and was removed in version 4.0. It’s vulnerable to a number of attacks. See Working with big files for more information.
The VARBLOCK file format allows us to encrypt files that are larger than the RSA key. The format is as follows;  denotes byte string concatenation:
VARBLOCK := VERSION  BLOCK  BLOCK  ...
VERSION := 1
BLOCK := LENGTH  DATA
LENGTH := varintencoded length of the following data, in bytes
DATA := the data to store in the block
The varintformat was taken from Google’s Protobuf, and allows us to efficiently encode an arbitrarily long integer.
8.4. Module: rsa.core¶
At the core of the RSA encryption method lie these functions. They both operate on (arbitrarily long) integers only. They probably aren’t of much use to you, but I wanted to document them anyway as they are the core of the entire library.

rsa.core.
encrypt_int
(message, ekey, n)¶ Encrypts a message using encryption key ‘ekey’, working modulo n

rsa.core.
decrypt_int
(cyphertext, dkey, n)¶ Decrypts a cypher text using the decryption key ‘dkey’, working modulo n