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| 1 | +// Copyright 2025 Contributors to the Parsec project. |
| 2 | +// SPDX-License-Identifier: Apache-2.0 |
| 3 | + |
| 4 | +use core::{ |
| 5 | + marker::PhantomData, |
| 6 | + ops::{Add, Mul}, |
| 7 | +}; |
| 8 | + |
| 9 | +use aes::cipher::AsyncStreamCipher; |
| 10 | +use cfb_mode::cipher::BlockCipherEncrypt; |
| 11 | +use digest::{ |
| 12 | + array::ArraySize, |
| 13 | + consts::{B1, U8}, |
| 14 | + crypto_common::{Iv, KeyIvInit, KeySizeUser}, |
| 15 | + typenum::{ |
| 16 | + operator_aliases::{Add1, Sum}, |
| 17 | + Unsigned, |
| 18 | + }, |
| 19 | + Digest, DynDigest, FixedOutputReset, Key, KeyInit, Mac, OutputSizeUser, |
| 20 | +}; |
| 21 | +use ecdsa::elliptic_curve::{ |
| 22 | + ecdh::{EphemeralSecret, SharedSecret}, |
| 23 | + sec1::{Coordinates, FromEncodedPoint, ModulusSize, ToEncodedPoint}, |
| 24 | + AffinePoint, Curve, CurveArithmetic, FieldBytesSize, PublicKey, |
| 25 | +}; |
| 26 | +use hmac::{EagerHash, Hmac}; |
| 27 | +use log::error; |
| 28 | +use rand::{thread_rng, Rng}; |
| 29 | +use rsa::{Oaep, RsaPublicKey}; |
| 30 | + |
| 31 | +use crate::{ |
| 32 | + error::{Error, Result, WrapperErrorKind}, |
| 33 | + structures::{EncryptedSecret, IdObject, Name}, |
| 34 | + utils::kdf::{self}, |
| 35 | +}; |
| 36 | + |
| 37 | +// [`TpmHmac`] intends to code for the key expected for hmac |
| 38 | +// in the KDFa and KDFe derivations. There are no standard sizes for hmac keys really, |
| 39 | +// upstream RustCrypto considers it to be [BlockSize], but TPM specification |
| 40 | +// has a different opinion on the matter, and expect the key to the output |
| 41 | +// bit size of the hash algorithm used. |
| 42 | +// |
| 43 | +// See https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-1-Architecture.pdf#page=202 |
| 44 | +// section 24.5 HMAC: |
| 45 | +// bits the number of bits in the digest produced by ekNameAlg |
| 46 | +// |
| 47 | +// [BlockSize]: https://docs.rs/hmac/0.12.1/hmac/struct.HmacCore.html#impl-KeySizeUser-for-HmacCore%3CD%3E |
| 48 | +struct TpmHmac<H>(PhantomData<H>); |
| 49 | + |
| 50 | +impl<H> KeySizeUser for TpmHmac<H> |
| 51 | +where |
| 52 | + H: OutputSizeUser, |
| 53 | +{ |
| 54 | + type KeySize = H::OutputSize; |
| 55 | +} |
| 56 | + |
| 57 | +pub fn make_credential_ecc<C, EkHash, EkCipher>( |
| 58 | + ek_public: PublicKey<C>, |
| 59 | + secret: &[u8], |
| 60 | + key_name: Name, |
| 61 | +) -> Result<(IdObject, EncryptedSecret)> |
| 62 | +where |
| 63 | + C: Curve + CurveArithmetic, |
| 64 | + |
| 65 | + AffinePoint<C>: FromEncodedPoint<C> + ToEncodedPoint<C>, |
| 66 | + FieldBytesSize<C>: ModulusSize, |
| 67 | + |
| 68 | + <FieldBytesSize<C> as Add>::Output: Add<FieldBytesSize<C>>, |
| 69 | + Sum<FieldBytesSize<C>, FieldBytesSize<C>>: ArraySize, |
| 70 | + Sum<FieldBytesSize<C>, FieldBytesSize<C>>: Add<U8>, |
| 71 | + Sum<Sum<FieldBytesSize<C>, FieldBytesSize<C>>, U8>: Add<B1>, |
| 72 | + Add1<Sum<Sum<FieldBytesSize<C>, FieldBytesSize<C>>, U8>>: ArraySize, |
| 73 | + |
| 74 | + EkHash: Digest + EagerHash + FixedOutputReset, |
| 75 | + <EkHash as OutputSizeUser>::OutputSize: Mul<U8>, |
| 76 | + <<EkHash as OutputSizeUser>::OutputSize as Mul<U8>>::Output: Unsigned, |
| 77 | + <<EkHash as EagerHash>::Core as OutputSizeUser>::OutputSize: ArraySize + Mul<U8>, |
| 78 | + <<<EkHash as EagerHash>::Core as OutputSizeUser>::OutputSize as Mul<U8>>::Output: Unsigned, |
| 79 | + |
| 80 | + EkCipher: KeySizeUser + BlockCipherEncrypt + KeyInit, |
| 81 | + <EkCipher as KeySizeUser>::KeySize: Mul<U8>, |
| 82 | + <<EkCipher as KeySizeUser>::KeySize as Mul<U8>>::Output: ArraySize, |
| 83 | +{ |
| 84 | + let mut rng = thread_rng(); |
| 85 | + |
| 86 | + // See Table 22 - Key Generation for the various labels used here after: |
| 87 | + // https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-1-Architecture.pdf#page=183 |
| 88 | + |
| 89 | + // C.6.4. ECC Secret Sharing for Credentials |
| 90 | + // https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-1-Architecture.pdf#page=311 |
| 91 | + let local = EphemeralSecret::<C>::random(&mut rng); |
| 92 | + |
| 93 | + let ecdh_secret: SharedSecret<C> = local.diffie_hellman(&ek_public); |
| 94 | + let local_public = local.public_key(); |
| 95 | + drop(local); |
| 96 | + |
| 97 | + let seed = kdf::kdfe::<kdf::Identity, EkHash, C, TpmHmac<EkHash>>( |
| 98 | + &ecdh_secret, |
| 99 | + &local_public, |
| 100 | + &ek_public, |
| 101 | + )?; |
| 102 | + drop(ecdh_secret); |
| 103 | + |
| 104 | + // The local ECDH pair is used as "encrypted seed" |
| 105 | + let encoded_point = local_public.to_encoded_point(false); |
| 106 | + let Coordinates::Uncompressed { |
| 107 | + x: point_x, |
| 108 | + y: point_y, |
| 109 | + } = encoded_point.coordinates() |
| 110 | + else { |
| 111 | + // NOTE: The only way this could trigger would be for the local key to be identity. |
| 112 | + error!("Couldn't compute coordinates for the local public key"); |
| 113 | + return Err(Error::local_error(WrapperErrorKind::InvalidParam)); |
| 114 | + }; |
| 115 | + let encrypted_seed = { |
| 116 | + let mut out = vec![]; |
| 117 | + out.extend_from_slice(&FieldBytesSize::<C>::U16.to_be_bytes()[..]); |
| 118 | + out.extend_from_slice(&point_x); |
| 119 | + out.extend_from_slice(&FieldBytesSize::<C>::U16.to_be_bytes()[..]); |
| 120 | + out.extend_from_slice(&point_y); |
| 121 | + out |
| 122 | + }; |
| 123 | + let encrypted_secret = EncryptedSecret::from_bytes(&encrypted_seed)?; |
| 124 | + |
| 125 | + let id_object = secret_to_credential::<EkHash, EkCipher>(seed, secret, key_name)?; |
| 126 | + |
| 127 | + Ok((id_object, encrypted_secret)) |
| 128 | +} |
| 129 | + |
| 130 | +pub fn make_credential_rsa<EkHash, EkCipher>( |
| 131 | + ek_public: &RsaPublicKey, |
| 132 | + secret: &[u8], |
| 133 | + key_name: Name, |
| 134 | +) -> Result<(IdObject, EncryptedSecret)> |
| 135 | +where |
| 136 | + EkHash: Digest + DynDigest + Send + Sync + 'static, |
| 137 | + EkHash: EagerHash + FixedOutputReset, |
| 138 | + <EkHash as OutputSizeUser>::OutputSize: Mul<U8>, |
| 139 | + <<EkHash as OutputSizeUser>::OutputSize as Mul<U8>>::Output: Unsigned, |
| 140 | + <<EkHash as EagerHash>::Core as OutputSizeUser>::OutputSize: ArraySize + Mul<U8>, |
| 141 | + <<<EkHash as EagerHash>::Core as OutputSizeUser>::OutputSize as Mul<U8>>::Output: Unsigned, |
| 142 | + |
| 143 | + EkCipher: KeySizeUser + BlockCipherEncrypt + KeyInit, |
| 144 | + <EkCipher as KeySizeUser>::KeySize: Mul<U8>, |
| 145 | + <<EkCipher as KeySizeUser>::KeySize as Mul<U8>>::Output: ArraySize, |
| 146 | +{ |
| 147 | + let mut rng = thread_rng(); |
| 148 | + |
| 149 | + // See Table 22 - Key Generation for the various labels used here after: |
| 150 | + // https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-1-Architecture.pdf#page=183 |
| 151 | + |
| 152 | + // B.10.4 RSA Secret Sharing for Credentials |
| 153 | + // https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-1-Architecture.pdf#page=302 |
| 154 | + let random_seed = { |
| 155 | + let mut out = Key::<TpmHmac<EkHash>>::default(); |
| 156 | + rng.try_fill(out.as_mut_slice()).map_err(|e| { |
| 157 | + error!("RNG error: {e}"); |
| 158 | + Error::local_error(WrapperErrorKind::InternalError) |
| 159 | + })?; |
| 160 | + out |
| 161 | + }; |
| 162 | + |
| 163 | + // The random seed is then encrypted with RSA-OAEP |
| 164 | + // |
| 165 | + // B.4 RSAES_OAEP |
| 166 | + // https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-1-Architecture.pdf#page=297 |
| 167 | + // |
| 168 | + // The label is a byte-stream whose last byte must be zero |
| 169 | + // |
| 170 | + // B.10.4. RSA Secret Sharing for Credentials |
| 171 | + // https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-1-Architecture.pdf#page=302 |
| 172 | + // |
| 173 | + // The label is going to be "IDENTITY" for secret sharing. |
| 174 | + let encrypted_seed = { |
| 175 | + let padding = Oaep::new_with_label::<EkHash, _>(b"IDENTITY\0".to_vec()); |
| 176 | + let enc_data = ek_public |
| 177 | + .encrypt(&mut rng, padding, &random_seed[..]) |
| 178 | + .map_err(|e| { |
| 179 | + error!("RSA OAEP encryption error: {e}"); |
| 180 | + Error::local_error(WrapperErrorKind::InternalError) |
| 181 | + })?; |
| 182 | + enc_data |
| 183 | + }; |
| 184 | + let encrypted_secret = EncryptedSecret::from_bytes(&encrypted_seed)?; |
| 185 | + |
| 186 | + let id_object = secret_to_credential::<EkHash, EkCipher>(random_seed, secret, key_name)?; |
| 187 | + |
| 188 | + Ok((id_object, encrypted_secret)) |
| 189 | +} |
| 190 | + |
| 191 | +fn secret_to_credential<EkHash, EkCipher>( |
| 192 | + seed: Key<TpmHmac<EkHash>>, |
| 193 | + secret: &[u8], |
| 194 | + key_name: Name, |
| 195 | +) -> Result<IdObject> |
| 196 | +where |
| 197 | + EkHash: Digest + EagerHash + FixedOutputReset, |
| 198 | + <EkHash as OutputSizeUser>::OutputSize: Mul<U8>, |
| 199 | + <<EkHash as OutputSizeUser>::OutputSize as Mul<U8>>::Output: Unsigned, |
| 200 | + <<EkHash as EagerHash>::Core as OutputSizeUser>::OutputSize: ArraySize + Mul<U8>, |
| 201 | + <<<EkHash as EagerHash>::Core as OutputSizeUser>::OutputSize as Mul<U8>>::Output: Unsigned, |
| 202 | + |
| 203 | + EkCipher: KeySizeUser + BlockCipherEncrypt + KeyInit, |
| 204 | + <EkCipher as KeySizeUser>::KeySize: Mul<U8>, |
| 205 | + <<EkCipher as KeySizeUser>::KeySize as Mul<U8>>::Output: ArraySize, |
| 206 | +{ |
| 207 | + // Prepare the sensitive data |
| 208 | + // this will be then encrypted using AES-CFB (size of the symmetric key depends on the EK). |
| 209 | + let mut sensitive_data = { |
| 210 | + let mut out = vec![]; |
| 211 | + out.extend_from_slice( |
| 212 | + &u16::try_from(secret.len()) |
| 213 | + .map_err(|_| { |
| 214 | + error!("secret may only be 2^16 bytes long"); |
| 215 | + Error::local_error(WrapperErrorKind::WrongParamSize) |
| 216 | + })? |
| 217 | + .to_be_bytes()[..], |
| 218 | + ); |
| 219 | + out.extend_from_slice(secret); |
| 220 | + out |
| 221 | + }; |
| 222 | + |
| 223 | + // We'll now encrypt the sensitive data, and hmac the result of the encryption |
| 224 | + // https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-1-Architecture.pdf#page=201 |
| 225 | + // See 24.4 Symmetric Encryption |
| 226 | + let sym_key = kdf::kdfa::<EkHash, kdf::Storage, EkCipher>(&seed, key_name.value(), &[])?; |
| 227 | + |
| 228 | + // TODO(baloo): once the weak key detection merges |
| 229 | + // https://github.com/RustCrypto/traits/pull/1739 |
| 230 | + // https://github.com/RustCrypto/block-ciphers/pull/465 |
| 231 | + // |
| 232 | + // We should check for weak keys, and re-run all the steps above until we get a non-weak key |
| 233 | + // this is to be in compliance with TPM spec section 11.4.10.4: |
| 234 | + // https://trustedcomputinggroup.org/wp-content/uploads/TPM-2.0-1.83-Part-1-Architecture.pdf#page=82 |
| 235 | + |
| 236 | + let iv: Iv<cfb_mode::Encryptor<EkCipher>> = Default::default(); |
| 237 | + |
| 238 | + cfb_mode::Encryptor::<EkCipher>::new(&sym_key.into(), &iv.into()).encrypt(&mut sensitive_data); |
| 239 | + |
| 240 | + // See 24.5 HMAC |
| 241 | + let hmac_key = kdf::kdfa::<EkHash, kdf::Integrity, TpmHmac<EkHash>>(&seed, &[], &[])?; |
| 242 | + let mut hmac = Hmac::<EkHash>::new_from_slice(&hmac_key).map_err(|e| { |
| 243 | + error!("HMAC initialization error: {e}"); |
| 244 | + Error::local_error(WrapperErrorKind::WrongParamSize) |
| 245 | + })?; |
| 246 | + Mac::update(&mut hmac, &sensitive_data); |
| 247 | + Mac::update(&mut hmac, key_name.value()); |
| 248 | + let hmac = hmac.finalize(); |
| 249 | + |
| 250 | + // We'll now serialize the object and get everything through the door. |
| 251 | + let mut out = vec![]; |
| 252 | + out.extend_from_slice( |
| 253 | + &u16::try_from(hmac.into_bytes().len()) |
| 254 | + .map_err(|_| { |
| 255 | + // NOTE: this shouldn't ever trigger ... but ... |
| 256 | + error!("HMAC output may only be 2^16 bytes long"); |
| 257 | + Error::local_error(WrapperErrorKind::WrongParamSize) |
| 258 | + })? |
| 259 | + .to_be_bytes()[..], |
| 260 | + ); |
| 261 | + out.extend_from_slice(&hmac.into_bytes()); |
| 262 | + out.extend_from_slice(&sensitive_data); |
| 263 | + |
| 264 | + IdObject::from_bytes(&out) |
| 265 | +} |
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