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"""ASN1 encoding helpers for converting between PKCS1 and PKCS8.
Required by rsa_backend but not cryptography_backend.
"""
from pyasn1.codec.der import decoder, encoder
from pyasn1.type import namedtype, univ
RSA_ENCRYPTION_ASN1_OID = "1.2.840.113549.1.1.1"
class RsaAlgorithmIdentifier(univ.Sequence):
"""ASN1 structure for recording RSA PrivateKeyAlgorithm identifiers."""
componentType = namedtype.NamedTypes(
namedtype.NamedType("rsaEncryption", univ.ObjectIdentifier()), namedtype.NamedType("parameters", univ.Null())
)
class PKCS8PrivateKey(univ.Sequence):
"""ASN1 structure for recording PKCS8 private keys."""
componentType = namedtype.NamedTypes(
namedtype.NamedType("version", univ.Integer()),
namedtype.NamedType("privateKeyAlgorithm", RsaAlgorithmIdentifier()),
namedtype.NamedType("privateKey", univ.OctetString()),
)
class PublicKeyInfo(univ.Sequence):
"""ASN1 structure for recording PKCS8 public keys."""
componentType = namedtype.NamedTypes(
namedtype.NamedType("algorithm", RsaAlgorithmIdentifier()), namedtype.NamedType("publicKey", univ.BitString())
)
def rsa_private_key_pkcs8_to_pkcs1(pkcs8_key):
"""Convert a PKCS8-encoded RSA private key to PKCS1."""
decoded_values = decoder.decode(pkcs8_key, asn1Spec=PKCS8PrivateKey())
try:
decoded_key = decoded_values[0]
except IndexError:
raise ValueError("Invalid private key encoding")
return decoded_key["privateKey"]
def rsa_private_key_pkcs1_to_pkcs8(pkcs1_key):
"""Convert a PKCS1-encoded RSA private key to PKCS8."""
algorithm = RsaAlgorithmIdentifier()
algorithm["rsaEncryption"] = RSA_ENCRYPTION_ASN1_OID
pkcs8_key = PKCS8PrivateKey()
pkcs8_key["version"] = 0
pkcs8_key["privateKeyAlgorithm"] = algorithm
pkcs8_key["privateKey"] = pkcs1_key
return encoder.encode(pkcs8_key)
def rsa_public_key_pkcs1_to_pkcs8(pkcs1_key):
"""Convert a PKCS1-encoded RSA private key to PKCS8."""
algorithm = RsaAlgorithmIdentifier()
algorithm["rsaEncryption"] = RSA_ENCRYPTION_ASN1_OID
pkcs8_key = PublicKeyInfo()
pkcs8_key["algorithm"] = algorithm
pkcs8_key["publicKey"] = univ.BitString.fromOctetString(pkcs1_key)
return encoder.encode(pkcs8_key)
def rsa_public_key_pkcs8_to_pkcs1(pkcs8_key):
"""Convert a PKCS8-encoded RSA private key to PKCS1."""
decoded_values = decoder.decode(pkcs8_key, asn1Spec=PublicKeyInfo())
try:
decoded_key = decoded_values[0]
except IndexError:
raise ValueError("Invalid public key encoding.")
return decoded_key["publicKey"].asOctets()
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