apkdmverity/src/apksigv4.rs

/*
 * Copyright (C) 2021 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

use anyhow::{anyhow, Context, Result};
use num_derive::FromPrimitive;
use num_traits::FromPrimitive;
use std::io::{Read, Seek};

// `apksigv4` module provides routines to decode the idsig file as defined in [APK signature
// scheme v4] (https://source.android.com/security/apksigning/v4).

#[derive(Debug)]
pub struct V4Signature {
    pub version: Version,
    pub hashing_info: HashingInfo,
    pub signing_info: SigningInfo,
    pub merkle_tree_size: u32,
    pub merkle_tree_offset: u64,
}

#[derive(Debug)]
pub struct HashingInfo {
    pub hash_algorithm: HashAlgorithm,
    pub log2_blocksize: u8,
    pub salt: Box<[u8]>,
    pub raw_root_hash: Box<[u8]>,
}

#[derive(Debug)]
pub struct SigningInfo {
    pub apk_digest: Box<[u8]>,
    pub x509_certificate: Box<[u8]>,
    pub additional_data: Box<[u8]>,
    pub public_key: Box<[u8]>,
    pub signature_algorithm_id: SignatureAlgorithmId,
    pub signature: Box<[u8]>,
}

#[derive(Debug, PartialEq, FromPrimitive)]
#[repr(u32)]
pub enum Version {
    V2 = 2,
}

impl Version {
    fn from(val: u32) -> Result<Version> {
        Self::from_u32(val).ok_or_else(|| anyhow!("{} is an unsupported version", val))
    }
}

#[derive(Debug, PartialEq, FromPrimitive)]
#[repr(u32)]
pub enum HashAlgorithm {
    SHA256 = 1,
}

impl HashAlgorithm {
    fn from(val: u32) -> Result<HashAlgorithm> {
        Self::from_u32(val).ok_or_else(|| anyhow!("{} is an unsupported hash algorithm", val))
    }
}

#[derive(Debug, PartialEq, FromPrimitive)]
#[allow(non_camel_case_types)]
#[repr(u32)]
pub enum SignatureAlgorithmId {
    RSASSA_PSS_SHA2_256 = 0x0101,
    RSASSA_PSS_SHA2_512 = 0x0102,
    RSASSA_PKCS1_SHA2_256 = 0x0103,
    RSASSA_PKCS1_SHA2_512 = 0x0104,
    ECDSA_SHA2_256 = 0x0201,
    ECDSA_SHA2_512 = 0x0202,
    DSA_SHA2_256 = 0x0301,
}

impl SignatureAlgorithmId {
    fn from(val: u32) -> Result<SignatureAlgorithmId> {
        Self::from_u32(val)
            .with_context(|| format!("{:#06x} is an unsupported signature algorithm", val))
    }
}

impl V4Signature {
    /// Reads a stream from `r` and then parses it into a `V4Signature` struct.
    pub fn from<T: Read + Seek>(mut r: T) -> Result<V4Signature> {
        Ok(V4Signature {
            version: Version::from(read_le_u32(&mut r)?)?,
            hashing_info: HashingInfo::from(&mut r)?,
            signing_info: SigningInfo::from(&mut r)?,
            merkle_tree_size: read_le_u32(&mut r)?,
            merkle_tree_offset: r.stream_position()?,
        })
    }
}

impl HashingInfo {
    fn from(mut r: &mut dyn Read) -> Result<HashingInfo> {
        read_le_u32(&mut r)?;
        Ok(HashingInfo {
            hash_algorithm: HashAlgorithm::from(read_le_u32(&mut r)?)?,
            log2_blocksize: read_u8(&mut r)?,
            salt: read_sized_array(&mut r)?,
            raw_root_hash: read_sized_array(&mut r)?,
        })
    }
}

impl SigningInfo {
    fn from(mut r: &mut dyn Read) -> Result<SigningInfo> {
        read_le_u32(&mut r)?;
        Ok(SigningInfo {
            apk_digest: read_sized_array(&mut r)?,
            x509_certificate: read_sized_array(&mut r)?,
            additional_data: read_sized_array(&mut r)?,
            public_key: read_sized_array(&mut r)?,
            signature_algorithm_id: SignatureAlgorithmId::from(read_le_u32(&mut r)?)?,
            signature: read_sized_array(&mut r)?,
        })
    }
}

fn read_u8(r: &mut dyn Read) -> Result<u8> {
    let mut byte = [0; 1];
    r.read_exact(&mut byte)?;
    Ok(byte[0])
}

fn read_le_u32(r: &mut dyn Read) -> Result<u32> {
    let mut bytes = [0; 4];
    r.read_exact(&mut bytes)?;
    Ok(u32::from_le_bytes(bytes))
}

fn read_sized_array(r: &mut dyn Read) -> Result<Box<[u8]>> {
    let size = read_le_u32(r)?;
    let mut data = vec![0; size as usize];
    r.read_exact(&mut data)?;
    Ok(data.into_boxed_slice())
}

#[cfg(test)]
mod tests {
    use crate::util::hexstring_from;
    use crate::*;
    use std::io::Cursor;

    #[test]
    fn parse_idsig_file() {
        let idsig = Cursor::new(include_bytes!("../testdata/test.apk.idsig"));
        let parsed = V4Signature::from(idsig).unwrap();

        assert_eq!(Version::V2, parsed.version);

        let hi = parsed.hashing_info;
        assert_eq!(HashAlgorithm::SHA256, hi.hash_algorithm);
        assert_eq!(12, hi.log2_blocksize);
        assert_eq!("", hexstring_from(hi.salt.as_ref()));
        assert_eq!(
            "ce1194fdb3cb2537daf0ac8cdf4926754adcbce5abeece7945fe25d204a0df6a",
            hexstring_from(hi.raw_root_hash.as_ref())
        );

        let si = parsed.signing_info;
        assert_eq!(
            "b5225523a813fb84ed599dd649698c080bcfed4fb19ddb00283a662a2683bc15",
            hexstring_from(si.apk_digest.as_ref())
        );
        assert_eq!("", hexstring_from(si.additional_data.as_ref()));
        assert_eq!(
            "303d021c77304d0f4732a90372bbfce095223e4ba82427ceb381f69bc6762d78021d008b99924\
                   a8585c38d7f654835eb219ae9e176b44e86dcb23153e3d9d6",
            hexstring_from(si.signature.as_ref())
        );
        assert_eq!(SignatureAlgorithmId::DSA_SHA2_256, si.signature_algorithm_id);

        assert_eq!(36864, parsed.merkle_tree_size);
        assert_eq!(2251, parsed.merkle_tree_offset);
    }
}