Namespace: go.std.crypto.rsa
v1.0Contents
Summary
Provides a lowlevel interface to the crypto/rsa package.
Package rsa implements RSA encryption as specified in PKCS #1 and RFC 8017.
RSA is a single, fundamental operation that is used in this package to
implement either publickey encryption or publickey signatures.
The original specification for encryption and signatures with RSA is PKCS #1
and the terms "RSA encryption" and "RSA signatures" by default refer to
PKCS #1 version 1.5. However, that specification has flaws and new designs
should use version 2, usually called by just OAEP and PSS, where
possible.
Two sets of interfaces are included in this package. When a more abstract
interface isn't necessary, there are functions for encrypting/decrypting
with v1.5/OAEP and signing/verifying with v1.5/PSS. If one needs to abstract
over the public key primitive, the PrivateKey type implements the
Decrypter and Signer interfaces from the crypto package.
The RSA operations in this package are not implemented using constanttime algorithms.
Index
 CRTValue
 DecryptOAEP
 DecryptPKCS1v15
 DecryptPKCS1v15SessionKey
 EncryptOAEP
 EncryptPKCS1v15
 ErrDecryption
 ErrMessageTooLong
 ErrVerification
 GenerateKey
 GenerateMultiPrimeKey
 OAEPOptions
 PKCS1v15DecryptOptions
 PSSOptions
 PSSSaltLengthAuto
 PSSSaltLengthEqualsHash
 PrecomputedValues
 PrivateKey
 PublicKey
 SignPKCS1v15
 SignPSS
 VerifyPKCS1v15
 VerifyPSS
 arrayOfCRTValue
 arrayOfOAEPOptions
 arrayOfPKCS1v15DecryptOptions
 arrayOfPSSOptions
 arrayOfPrecomputedValues
 arrayOfPrivateKey
 arrayOfPublicKey
 refToCRTValue
 refToOAEPOptions
 refToPKCS1v15DecryptOptions
 refToPSSOptions
 refToPrecomputedValues
 refToPrivateKey
 refToPublicKey
Legend

Constant
Variable
Function
Macro
Special form
Type
GoVar
Receiver/Method
Constants
Constants are variables with :const true in their metadata. Joker currently does not recognize them as special; as such, it allows redefining them or their values.
PSSSaltLengthAuto
Int v1.0PSSSaltLengthAuto causes the salt in a PSS signature to be as large
as possible when signing, and to be autodetected when verifying.

PSSSaltLengthEqualsHash
Int v1.0PSSSaltLengthEqualsHash causes the salt length to equal the length
of the hash used in the signature.
Variables

ErrDecryption
Var v1.0ErrDecryption represents a failure to decrypt a message.
It is deliberately vague to avoid adaptive attacks.

ErrMessageTooLong
Var v1.0ErrMessageTooLong is returned when attempting to encrypt a message which is
too large for the size of the public key.

ErrVerification
Var v1.0ErrVerification represents a failure to verify a signature.
It is deliberately vague to avoid adaptive attacks.
Functions, Macros, and Special Forms

DecryptOAEP
Function v1.0(DecryptOAEP hash random priv ciphertext label)
DecryptOAEP decrypts ciphertext using RSAOAEP.
OAEP is parameterised by a hash function that is used as a random oracle.
Encryption and decryption of a given message must use the same hash function
and sha256.New() is a reasonable choice.
The random parameter, if not nil, is used to blind the privatekey operation
and avoid timing sidechannel attacks. Blinding is purely internal to this
function – the random data need not match that used when encrypting.
The label parameter must match the value given when encrypting. See
EncryptOAEP for details.
Go input arguments: (hash hash.Hash, random io.Reader, priv *PrivateKey, ciphertext []byte, label []byte)
Go returns: ([]byte, error)
Joker input arguments: [^go.std.hash/Hash hash, ^go.std.io/Reader random, ^refToPrivateKey priv, ^arrayOfByte ciphertext, ^arrayOfByte label]
Joker returns: [^arrayOfByte, ^Error] 
DecryptPKCS1v15
Function v1.0(DecryptPKCS1v15 rand priv ciphertext)
DecryptPKCS1v15 decrypts a plaintext using RSA and the padding scheme from PKCS #1 v1.5.
If rand != nil, it uses RSA blinding to avoid timing sidechannel attacks.
Note that whether this function returns an error or not discloses secret
information. If an attacker can cause this function to run repeatedly and
learn whether each instance returned an error then they can decrypt and
forge signatures as if they had the private key. See
DecryptPKCS1v15SessionKey for a way of solving this problem.
Go input arguments: (rand io.Reader, priv *PrivateKey, ciphertext []byte)
Go returns: ([]byte, error)
Joker input arguments: [^go.std.io/Reader rand, ^refToPrivateKey priv, ^arrayOfByte ciphertext]
Joker returns: [^arrayOfByte, ^Error] 
DecryptPKCS1v15SessionKey
Function v1.0(DecryptPKCS1v15SessionKey rand priv ciphertext key)
DecryptPKCS1v15SessionKey decrypts a session key using RSA and the padding scheme from PKCS #1 v1.5.
If rand != nil, it uses RSA blinding to avoid timing sidechannel attacks.
It returns an error if the ciphertext is the wrong length or if the
ciphertext is greater than the public modulus. Otherwise, no error is
returned. If the padding is valid, the resulting plaintext message is copied
into key. Otherwise, key is unchanged. These alternatives occur in constant
time. It is intended that the user of this function generate a random
session key beforehand and continue the protocol with the resulting value.
This will remove any possibility that an attacker can learn any information
about the plaintext.
See ``Chosen Ciphertext Attacks Against Protocols Based on the RSA
Encryption Standard PKCS #1'', Daniel Bleichenbacher, Advances in Cryptology
(Crypto '98).
Note that if the session key is too small then it may be possible for an
attacker to bruteforce it. If they can do that then they can learn whether
a random value was used (because it'll be different for the same ciphertext)
and thus whether the padding was correct. This defeats the point of this
function. Using at least a 16byte key will protect against this attack.
Go input arguments: (rand io.Reader, priv *PrivateKey, ciphertext []byte, key []byte)
Go returns: error
Joker input arguments: [^go.std.io/Reader rand, ^refToPrivateKey priv, ^arrayOfByte ciphertext, ^arrayOfByte key]
Joker returns: ^Error 
EncryptOAEP
Function v1.0(EncryptOAEP hash random pub msg label)
EncryptOAEP encrypts the given message with RSAOAEP.
OAEP is parameterised by a hash function that is used as a random oracle.
Encryption and decryption of a given message must use the same hash function
and sha256.New() is a reasonable choice.
The random parameter is used as a source of entropy to ensure that
encrypting the same message twice doesn't result in the same ciphertext.
The label parameter may contain arbitrary data that will not be encrypted,
but which gives important context to the message. For example, if a given
public key is used to decrypt two types of messages then distinct label
values could be used to ensure that a ciphertext for one purpose cannot be
used for another by an attacker. If not required it can be empty.
The message must be no longer than the length of the public modulus minus
twice the hash length, minus a further 2.
Go input arguments: (hash hash.Hash, random io.Reader, pub *PublicKey, msg []byte, label []byte)
Go returns: ([]byte, error)
Joker input arguments: [^go.std.hash/Hash hash, ^go.std.io/Reader random, ^refToPublicKey pub, ^arrayOfByte msg, ^arrayOfByte label]
Joker returns: [^arrayOfByte, ^Error] 
EncryptPKCS1v15
Function v1.0(EncryptPKCS1v15 rand pub msg)
EncryptPKCS1v15 encrypts the given message with RSA and the padding
scheme from PKCS #1 v1.5. The message must be no longer than the
length of the public modulus minus 11 bytes.
The rand parameter is used as a source of entropy to ensure that
encrypting the same message twice doesn't result in the same
ciphertext.
WARNING: use of this function to encrypt plaintexts other than
session keys is dangerous. Use RSA OAEP in new protocols.
Go input arguments: (rand io.Reader, pub *PublicKey, msg []byte)
Go returns: ([]byte, error)
Joker input arguments: [^go.std.io/Reader rand, ^refToPublicKey pub, ^arrayOfByte msg]
Joker returns: [^arrayOfByte, ^Error] 
GenerateKey
Function v1.0(GenerateKey random bits)
GenerateKey generates an RSA keypair of the given bit size using the
random source random (for example, crypto/rand.Reader).
Go input arguments: (random io.Reader, bits int)
Go returns: (*PrivateKey, error)
Joker input arguments: [^go.std.io/Reader random, ^Int bits]
Joker returns: [^refToPrivateKey, ^Error] 
GenerateMultiPrimeKey
Function v1.0(GenerateMultiPrimeKey random nprimes bits)
GenerateMultiPrimeKey generates a multiprime RSA keypair of the given bit
size and the given random source, as suggested in [1]. Although the public
keys are compatible (actually, indistinguishable) from the 2prime case,
the private keys are not. Thus it may not be possible to export multiprime
private keys in certain formats or to subsequently import them into other
code.
Table 1 in [2] suggests maximum numbers of primes for a given size.
[1] US patent 4405829 (1972, expired)
[2] http://www.cacr.math.uwaterloo.ca/techreports/2006/cacr200616.pdf
Go input arguments: (random io.Reader, nprimes int, bits int)
Go returns: (*PrivateKey, error)
Joker input arguments: [^go.std.io/Reader random, ^Int nprimes, ^Int bits]
Joker returns: [^refToPrivateKey, ^Error] 
SignPKCS1v15
Function v1.0(SignPKCS1v15 rand priv hash hashed)
SignPKCS1v15 calculates the signature of hashed using
RSASSAPKCS1V1_5SIGN from RSA PKCS #1 v1.5. Note that hashed must
be the result of hashing the input message using the given hash
function. If hash is zero, hashed is signed directly. This isn't
advisable except for interoperability.
If rand is not nil then RSA blinding will be used to avoid timing
sidechannel attacks.
This function is deterministic. Thus, if the set of possible
messages is small, an attacker may be able to build a map from
messages to signatures and identify the signed messages. As ever,
signatures provide authenticity, not confidentiality.
Go input arguments: (rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte)
Go returns: ([]byte, error)
Joker input arguments: [^go.std.io/Reader rand, ^refToPrivateKey priv, ^go.std.crypto/Hash hash, ^arrayOfByte hashed]
Joker returns: [^arrayOfByte, ^Error] 
SignPSS
Function v1.0(SignPSS rand priv hash digest opts)
SignPSS calculates the signature of digest using PSS.
digest must be the result of hashing the input message using the given hash
function. The opts argument may be nil, in which case sensible defaults are
used. If opts.Hash is set, it overrides hash.
Go input arguments: (rand io.Reader, priv *PrivateKey, hash crypto.Hash, digest []byte, opts *PSSOptions)
Go returns: ([]byte, error)
Joker input arguments: [^go.std.io/Reader rand, ^refToPrivateKey priv, ^go.std.crypto/Hash hash, ^arrayOfByte digest, ^refToPSSOptions opts]
Joker returns: [^arrayOfByte, ^Error] 
VerifyPKCS1v15
Function v1.0(VerifyPKCS1v15 pub hash hashed sig)
VerifyPKCS1v15 verifies an RSA PKCS #1 v1.5 signature.
hashed is the result of hashing the input message using the given hash
function and sig is the signature. A valid signature is indicated by
returning a nil error. If hash is zero then hashed is used directly. This
isn't advisable except for interoperability.
Go input arguments: (pub *PublicKey, hash crypto.Hash, hashed []byte, sig []byte)
Go returns: error
Joker input arguments: [^refToPublicKey pub, ^go.std.crypto/Hash hash, ^arrayOfByte hashed, ^arrayOfByte sig]
Joker returns: ^Error 
VerifyPSS
Function v1.0(VerifyPSS pub hash digest sig opts)
VerifyPSS verifies a PSS signature.
A valid signature is indicated by returning a nil error. digest must be the
result of hashing the input message using the given hash function. The opts
argument may be nil, in which case sensible defaults are used. opts.Hash is
ignored.
Go input arguments: (pub *PublicKey, hash crypto.Hash, digest []byte, sig []byte, opts *PSSOptions)
Go returns: error
Joker input arguments: [^refToPublicKey pub, ^go.std.crypto/Hash hash, ^arrayOfByte digest, ^arrayOfByte sig, ^refToPSSOptions opts]
Joker returns: ^Error
Types

CRTValue
Concrete Type v1.0CRTValue contains the precomputed Chinese remainder theorem values.

OAEPOptions
Concrete Type v1.0OAEPOptions is an interface for passing options to OAEP decryption using the
crypto.Decrypter interface.

PKCS1v15DecryptOptions
Concrete Type v1.0PKCS1v15DecrypterOpts is for passing options to PKCS #1 v1.5 decryption using
the crypto.Decrypter interface.

PSSOptions
Concrete Type v1.0PSSOptions contains options for creating and verifying PSS signatures.

PrecomputedValues
Concrete Type v1.0 
PrivateKey
Concrete Type v1.0A PrivateKey represents an RSA key

PublicKey
Concrete Type v1.0A PublicKey represents the public part of an RSA key.

arrayOfCRTValue
Concrete Type v1.0CRTValue contains the precomputed Chinese remainder theorem values.

arrayOfOAEPOptions
Concrete Type v1.0OAEPOptions is an interface for passing options to OAEP decryption using the
crypto.Decrypter interface.

arrayOfPKCS1v15DecryptOptions
Concrete Type v1.0PKCS1v15DecrypterOpts is for passing options to PKCS #1 v1.5 decryption using
the crypto.Decrypter interface.

arrayOfPSSOptions
Concrete Type v1.0PSSOptions contains options for creating and verifying PSS signatures.

arrayOfPrecomputedValues
Concrete Type v1.0 
arrayOfPrivateKey
Concrete Type v1.0A PrivateKey represents an RSA key

arrayOfPublicKey
Concrete Type v1.0A PublicKey represents the public part of an RSA key.

refToCRTValue
Concrete Type v1.0CRTValue contains the precomputed Chinese remainder theorem values.

refToOAEPOptions
Concrete Type v1.0OAEPOptions is an interface for passing options to OAEP decryption using the
crypto.Decrypter interface.

refToPKCS1v15DecryptOptions
Concrete Type v1.0PKCS1v15DecrypterOpts is for passing options to PKCS #1 v1.5 decryption using
the crypto.Decrypter interface.

refToPSSOptions
Concrete Type v1.0PSSOptions contains options for creating and verifying PSS signatures.

HashFunc
Receiver for refToPSSOptions v1.0([])
HashFunc returns opts.Hash so that PSSOptions implements crypto.SignerOpts.

refToPrecomputedValues
Concrete Type v1.0 
refToPrivateKey
Concrete Type v1.0A PrivateKey represents an RSA key

Decrypt
Receiver for refToPrivateKey v1.0([rand ciphertext opts])
Decrypt decrypts ciphertext with priv. If opts is nil or of type
*PKCS1v15DecryptOptions then PKCS #1 v1.5 decryption is performed. Otherwise
opts must have type *OAEPOptions and OAEP decryption is done.

Equal
Receiver for refToPrivateKey v1.0([x])
Equal reports whether priv and x have equivalent values. It ignores
Precomputed values.

Precompute
Receiver for refToPrivateKey v1.0([])
Precompute performs some calculations that speed up private key operations
in the future.

Public
Receiver for refToPrivateKey v1.0([])
Public returns the public key corresponding to priv.

Sign
Receiver for refToPrivateKey v1.0([rand digest opts])
Sign signs digest with priv, reading randomness from rand. If opts is a
*PSSOptions then the PSS algorithm will be used, otherwise PKCS #1 v1.5 will
be used. digest must be the result of hashing the input message using
opts.HashFunc().
This method implements crypto.Signer, which is an interface to support keys
where the private part is kept in, for example, a hardware module. Common
uses should use the Sign* functions in this package directly.

Validate
Receiver for refToPrivateKey v1.0([])
Validate performs basic sanity checks on the key.
It returns nil if the key is valid, or else an error describing a problem.

refToPublicKey
Concrete Type v1.0A PublicKey represents the public part of an RSA key.

Equal
Receiver for refToPublicKey v1.0([x])
Equal reports whether pub and x have the same value.

Size
Receiver for refToPublicKey v1.0([])
Size returns the modulus size in bytes. Raw signatures and ciphertexts
for or by this public key will have the same size.