diff --git a/apkverify/src/sigutil.rs b/apkverify/src/sigutil.rs
new file mode 100644
index 0000000..de3d0dd
--- /dev/null
+++ b/apkverify/src/sigutil.rs
@@ -0,0 +1,184 @@
+/*
+ * 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.
+ */
+
+//! Utilities for Signature Verification
+
+use anyhow::{anyhow, bail, Result};
+use byteorder::{LittleEndian, ReadBytesExt};
+use bytes::{Buf, Bytes};
+use std::io;
+use std::io::Read;
+use zip::spec::CentralDirectoryEnd as EndOfCentralDirectory;
+
+const APK_SIG_BLOCK_MIN_SIZE: u32 = 32;
+const APK_SIG_BLOCK_MAGIC: u128 = 0x3234206b636f6c4220676953204b5041;
+
+// TODO(jooyung): introduce type
+const SIGNATURE_RSA_PSS_WITH_SHA256: u32 = 0x0101;
+const SIGNATURE_RSA_PSS_WITH_SHA512: u32 = 0x0102;
+const SIGNATURE_RSA_PKCS1_V1_5_WITH_SHA256: u32 = 0x0103;
+const SIGNATURE_RSA_PKCS1_V1_5_WITH_SHA512: u32 = 0x0104;
+const SIGNATURE_ECDSA_WITH_SHA256: u32 = 0x0201;
+const SIGNATURE_ECDSA_WITH_SHA512: u32 = 0x0202;
+const SIGNATURE_DSA_WITH_SHA256: u32 = 0x0301;
+const SIGNATURE_VERITY_RSA_PKCS1_V1_5_WITH_SHA256: u32 = 0x0421;
+const SIGNATURE_VERITY_ECDSA_WITH_SHA256: u32 = 0x0423;
+const SIGNATURE_VERITY_DSA_WITH_SHA256: u32 = 0x0425;
+
+// TODO(jooyung): introduce type
+const CONTENT_DIGEST_CHUNKED_SHA256: u32 = 1;
+const CONTENT_DIGEST_CHUNKED_SHA512: u32 = 2;
+const CONTENT_DIGEST_VERITY_CHUNKED_SHA256: u32 = 3;
+#[allow(unused)]
+const CONTENT_DIGEST_SHA256: u32 = 4;
+
+pub struct SignatureInfo {
+    pub signing_block_offset: u32,
+    pub signature_block: Bytes,
+    pub eocd_offset: u32,
+    pub eocd: EndOfCentralDirectory,
+}
+
+/// Returns the APK Signature Scheme block contained in the provided file for the given ID
+/// and the additional information relevant for verifying the block against the file.
+pub fn find_signature<F: Read + io::Seek>(f: &mut F, block_id: u32) -> Result<SignatureInfo> {
+    let (eocd, eocd_offset) = EndOfCentralDirectory::find_and_parse(f)?;
+    if eocd.disk_number != eocd.disk_with_central_directory {
+        bail!("Support for multi-disk files is not implemented");
+    }
+    // TODO(jooyung): reject zip64 file
+    let (signing_block, signing_block_offset) =
+        find_signing_block(f, eocd.central_directory_offset)?;
+
+    // TODO(jooyung): propagate NotFound error so that verification can fallback to V2
+    let signature_scheme_block = find_signature_scheme_block(signing_block, block_id)?;
+    Ok(SignatureInfo {
+        signing_block_offset,
+        signature_block: signature_scheme_block,
+        eocd_offset: eocd_offset as u32,
+        eocd,
+    })
+}
+
+fn find_signing_block<T: Read + io::Seek>(
+    reader: &mut T,
+    central_directory_offset: u32,
+) -> Result<(Bytes, u32)> {
+    // FORMAT:
+    // OFFSET       DATA TYPE  DESCRIPTION
+    // * @+0  bytes uint64:    size in bytes (excluding this field)
+    // * @+8  bytes payload
+    // * @-24 bytes uint64:    size in bytes (same as the one above)
+    // * @-16 bytes uint128:   magic
+    if central_directory_offset < APK_SIG_BLOCK_MIN_SIZE {
+        bail!(
+            "APK too small for APK Signing Block. ZIP Central Directory offset: {}",
+            central_directory_offset
+        );
+    }
+    reader.seek(io::SeekFrom::Start((central_directory_offset - 24) as u64))?;
+    let size_in_footer = reader.read_u64::<LittleEndian>()? as u32;
+    if reader.read_u128::<LittleEndian>()? != APK_SIG_BLOCK_MAGIC {
+        bail!("No APK Signing Block before ZIP Central Directory")
+    }
+    let total_size = size_in_footer + 8;
+    let signing_block_offset = central_directory_offset
+        .checked_sub(total_size)
+        .ok_or_else(|| anyhow!("APK Signing Block size out of range: {}", size_in_footer))?;
+    reader.seek(io::SeekFrom::Start(signing_block_offset as u64))?;
+    let size_in_header = reader.read_u64::<LittleEndian>()? as u32;
+    if size_in_header != size_in_footer {
+        bail!(
+            "APK Signing Block sizes in header and footer do not match: {} vs {}",
+            size_in_header,
+            size_in_footer
+        );
+    }
+    reader.seek(io::SeekFrom::Start(signing_block_offset as u64))?;
+    let mut buf = vec![0u8; total_size as usize];
+    reader.read_exact(&mut buf)?;
+    Ok((Bytes::from(buf), signing_block_offset))
+}
+
+fn find_signature_scheme_block(buf: Bytes, block_id: u32) -> Result<Bytes> {
+    // FORMAT:
+    // OFFSET       DATA TYPE  DESCRIPTION
+    // * @+0  bytes uint64:    size in bytes (excluding this field)
+    // * @+8  bytes pairs
+    // * @-24 bytes uint64:    size in bytes (same as the one above)
+    // * @-16 bytes uint128:   magic
+    let mut pairs = buf.slice(8..(buf.len() - 24));
+    let mut entry_count = 0;
+    while pairs.has_remaining() {
+        entry_count += 1;
+        if pairs.remaining() < 8 {
+            bail!("Insufficient data to read size of APK Signing Block entry #{}", entry_count);
+        }
+        let length = pairs.get_u64_le();
+        let mut pair = pairs.split_to(length as usize);
+        let id = pair.get_u32_le();
+        if id == block_id {
+            return Ok(pair);
+        }
+    }
+    // TODO(jooyung): return NotFound error
+    bail!("No APK Signature Scheme block in APK Signing Block with ID: {}", block_id)
+}
+
+pub fn is_supported_signature_algorithm(algorithm_id: u32) -> bool {
+    match algorithm_id {
+        SIGNATURE_RSA_PSS_WITH_SHA256
+        | SIGNATURE_RSA_PSS_WITH_SHA512
+        | SIGNATURE_RSA_PKCS1_V1_5_WITH_SHA256
+        | SIGNATURE_RSA_PKCS1_V1_5_WITH_SHA512
+        | SIGNATURE_ECDSA_WITH_SHA256
+        | SIGNATURE_ECDSA_WITH_SHA512
+        | SIGNATURE_DSA_WITH_SHA256
+        | SIGNATURE_VERITY_RSA_PKCS1_V1_5_WITH_SHA256
+        | SIGNATURE_VERITY_ECDSA_WITH_SHA256
+        | SIGNATURE_VERITY_DSA_WITH_SHA256 => true,
+        _ => false,
+    }
+}
+
+fn to_content_digest_algorithm(algorithm_id: u32) -> Result<u32> {
+    match algorithm_id {
+        SIGNATURE_RSA_PSS_WITH_SHA256
+        | SIGNATURE_RSA_PKCS1_V1_5_WITH_SHA256
+        | SIGNATURE_ECDSA_WITH_SHA256
+        | SIGNATURE_DSA_WITH_SHA256 => Ok(CONTENT_DIGEST_CHUNKED_SHA256),
+        SIGNATURE_RSA_PSS_WITH_SHA512
+        | SIGNATURE_RSA_PKCS1_V1_5_WITH_SHA512
+        | SIGNATURE_ECDSA_WITH_SHA512 => Ok(CONTENT_DIGEST_CHUNKED_SHA512),
+        SIGNATURE_VERITY_RSA_PKCS1_V1_5_WITH_SHA256
+        | SIGNATURE_VERITY_ECDSA_WITH_SHA256
+        | SIGNATURE_VERITY_DSA_WITH_SHA256 => Ok(CONTENT_DIGEST_VERITY_CHUNKED_SHA256),
+        _ => bail!("Unknown signature algorithm: {}", algorithm_id),
+    }
+}
+
+pub fn rank_signature_algorithm(algo: u32) -> Result<u32> {
+    rank_content_digest_algorithm(to_content_digest_algorithm(algo)?)
+}
+
+fn rank_content_digest_algorithm(id: u32) -> Result<u32> {
+    match id {
+        CONTENT_DIGEST_CHUNKED_SHA256 => Ok(0),
+        CONTENT_DIGEST_VERITY_CHUNKED_SHA256 => Ok(1),
+        CONTENT_DIGEST_CHUNKED_SHA512 => Ok(2),
+        _ => bail!("Unknown digest algorithm: {}", id),
+    }
+}