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| 1 | +// Copyright 2019 Contributors to the Parsec project. |
| 2 | +// SPDX-License-Identifier: Apache-2.0 |
| 3 | + |
| 4 | +use aes::cipher::AsyncStreamCipher; |
| 5 | +use core::{marker::PhantomData, ops::Add}; |
| 6 | +use digest::{ |
| 7 | + array::ArraySize, |
| 8 | + consts::{B1, U8}, |
| 9 | + crypto_common::{Iv, KeyIvInit, KeySizeUser}, |
| 10 | + typenum::operator_aliases::{Add1, Sum}, |
| 11 | + KeyInit, Mac, OutputSizeUser, |
| 12 | +}; |
| 13 | +use ecdsa::elliptic_curve::{ |
| 14 | + ecdh::{EphemeralSecret, SharedSecret}, |
| 15 | + sec1::{FromEncodedPoint, ModulusSize, ToEncodedPoint}, |
| 16 | + AffinePoint, Curve, CurveArithmetic, FieldBytesSize, PublicKey, |
| 17 | +}; |
| 18 | +use hmac::Hmac; |
| 19 | +use rand::thread_rng; |
| 20 | +use sha2::Sha256; |
| 21 | + |
| 22 | +use crate::{ |
| 23 | + structures::{EncryptedSecret, IdObject, Name}, |
| 24 | + utils::kdf::{self}, |
| 25 | +}; |
| 26 | + |
| 27 | +// TpmHmacKey intends to code for the key expected for hmac |
| 28 | +// in the KDFa derivations. There are no standard sizes for hmac keys really, |
| 29 | +// upstream RustCrypto considers it to be BlockSize, but TPM specification |
| 30 | +// has a different opinion on the matter, and expect the key to the output |
| 31 | +// bit size of the hash algorithm used. |
| 32 | +// |
| 33 | +// See https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-1-Architecture.pdf#page=202 |
| 34 | +// section 24.5 HMAC: |
| 35 | +// bits the number of bits in the digest produced by ekNameAlg |
| 36 | +struct TpmHmac<H>(PhantomData<H>); |
| 37 | + |
| 38 | +impl<H> KeySizeUser for TpmHmac<H> |
| 39 | +where |
| 40 | + H: OutputSizeUser, |
| 41 | +{ |
| 42 | + type KeySize = H::OutputSize; |
| 43 | +} |
| 44 | + |
| 45 | +pub fn make_credential_ecc<C>( |
| 46 | + ek_public: PublicKey<C>, |
| 47 | + secret: &[u8], |
| 48 | + key_name: Name, |
| 49 | +) -> (IdObject, EncryptedSecret) |
| 50 | +where |
| 51 | + C: Curve + CurveArithmetic, |
| 52 | + |
| 53 | + AffinePoint<C>: FromEncodedPoint<C> + ToEncodedPoint<C>, |
| 54 | + FieldBytesSize<C>: ModulusSize, |
| 55 | + |
| 56 | + <FieldBytesSize<C> as Add>::Output: Add<FieldBytesSize<C>>, |
| 57 | + Sum<FieldBytesSize<C>, FieldBytesSize<C>>: ArraySize, |
| 58 | + Sum<FieldBytesSize<C>, FieldBytesSize<C>>: Add<U8>, |
| 59 | + Sum<Sum<FieldBytesSize<C>, FieldBytesSize<C>>, U8>: Add<B1>, |
| 60 | + Add1<Sum<Sum<FieldBytesSize<C>, FieldBytesSize<C>>, U8>>: ArraySize, |
| 61 | +{ |
| 62 | + let mut rng = thread_rng(); |
| 63 | + |
| 64 | + let local = EphemeralSecret::<C>::random(&mut rng); |
| 65 | + |
| 66 | + let ecdh_secret: SharedSecret<C> = local.diffie_hellman(&ek_public); |
| 67 | + |
| 68 | + type HmacSha256 = Hmac<Sha256>; |
| 69 | + |
| 70 | + let seed = kdf::kdfe::<kdf::Identity, Sha256, C, aes::Aes256>( |
| 71 | + &ecdh_secret, |
| 72 | + &local.public_key(), |
| 73 | + &ek_public, |
| 74 | + ); |
| 75 | + drop(ecdh_secret); |
| 76 | + |
| 77 | + // The local ECDH pair is used as "encrypted seed" |
| 78 | + let encrypted_seed = { |
| 79 | + let mut out = vec![]; |
| 80 | + out.extend_from_slice(&32u16.to_be_bytes()[..]); |
| 81 | + out.extend_from_slice(&local.public_key().to_encoded_point(false).x().unwrap()); |
| 82 | + out.extend_from_slice(&32u16.to_be_bytes()[..]); |
| 83 | + out.extend_from_slice(&local.public_key().to_encoded_point(false).y().unwrap()); |
| 84 | + out |
| 85 | + }; |
| 86 | + |
| 87 | + let mut sensitive_data = { |
| 88 | + let mut out = vec![]; |
| 89 | + out.extend_from_slice(&u16::try_from(secret.len()).unwrap().to_be_bytes()[..]); |
| 90 | + out.extend_from_slice(secret); |
| 91 | + out |
| 92 | + }; |
| 93 | + |
| 94 | + let sym_key = kdf::kdfa::<Sha256, kdf::Storage, aes::Aes128>(&seed, key_name.value(), &[]); |
| 95 | + let hmac_key = kdf::kdfa::<Sha256, kdf::Integrity, TpmHmac<Sha256>>(&seed, &[], &[]); |
| 96 | + |
| 97 | + type Aes128CfbEnc = cfb_mode::Encryptor<aes::Aes128>; |
| 98 | + let iv: Iv<Aes128CfbEnc> = Default::default(); |
| 99 | + |
| 100 | + Aes128CfbEnc::new(&sym_key.into(), &iv.into()).encrypt(&mut sensitive_data); |
| 101 | + |
| 102 | + let mut hmac = HmacSha256::new_from_slice(&hmac_key).unwrap(); |
| 103 | + hmac.update(&sensitive_data); |
| 104 | + hmac.update(key_name.value()); |
| 105 | + let hmac = hmac.finalize(); |
| 106 | + |
| 107 | + let mut out = vec![]; |
| 108 | + out.extend_from_slice( |
| 109 | + &u16::try_from(hmac.into_bytes().len()) |
| 110 | + .unwrap() |
| 111 | + .to_be_bytes()[..], |
| 112 | + ); |
| 113 | + out.extend_from_slice(&hmac.into_bytes()); |
| 114 | + out.extend_from_slice(&sensitive_data); |
| 115 | + |
| 116 | + ( |
| 117 | + IdObject::from_bytes(&out).unwrap(), |
| 118 | + EncryptedSecret::from_bytes(&encrypted_seed).unwrap(), |
| 119 | + ) |
| 120 | +} |
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