diff --git a/verity/Android.mk b/verity/Android.mk
index 018d40f..f166f9e 100644
--- a/verity/Android.mk
+++ b/verity/Android.mk
@@ -1,6 +1,15 @@
 LOCAL_PATH:= $(call my-dir)
 
 include $(CLEAR_VARS)
+LOCAL_MODULE := verify_boot_signature
+LOCAL_SRC_FILES := verify_boot_signature.c
+LOCAL_MODULE_CLASS := EXECUTABLES
+LOCAL_MODULE_TAGS := optional
+LOCAL_SHARED_LIBRARIES := libcrypto-host
+LOCAL_C_INCLUDES += external/openssl/include system/extras/ext4_utils system/core/mkbootimg
+include $(BUILD_HOST_EXECUTABLE)
+
+include $(CLEAR_VARS)
 LOCAL_MODULE := generate_verity_key
 LOCAL_SRC_FILES := generate_verity_key.c
 LOCAL_MODULE_CLASS := EXECUTABLES
diff --git a/verity/verify_boot_signature.c b/verity/verify_boot_signature.c
new file mode 100644
index 0000000..2274291
--- /dev/null
+++ b/verity/verify_boot_signature.c
@@ -0,0 +1,426 @@
+/*
+ * Copyright (C) 2014 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.
+ */
+
+#define _LARGEFILE64_SOURCE
+
+#include <endian.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <openssl/asn1.h>
+#include <openssl/asn1t.h>
+#include <openssl/err.h>
+#include <openssl/evp.h>
+#include <openssl/rsa.h>
+#include <openssl/x509.h>
+
+#include "bootimg.h"
+
+#define FORMAT_VERSION 1
+#define BUFFER_SIZE (1024 * 1024)
+
+typedef struct {
+    ASN1_STRING *target;
+    ASN1_INTEGER *length;
+} AuthAttrs;
+
+ASN1_SEQUENCE(AuthAttrs) = {
+    ASN1_SIMPLE(AuthAttrs, target, ASN1_PRINTABLE),
+    ASN1_SIMPLE(AuthAttrs, length, ASN1_INTEGER)
+} ASN1_SEQUENCE_END(AuthAttrs)
+
+IMPLEMENT_ASN1_FUNCTIONS(AuthAttrs)
+
+typedef struct {
+    ASN1_INTEGER *formatVersion;
+    X509 *certificate;
+    X509_ALGOR *algorithmIdentifier;
+    AuthAttrs *authenticatedAttributes;
+    ASN1_OCTET_STRING *signature;
+} BootSignature;
+
+ASN1_SEQUENCE(BootSignature) = {
+    ASN1_SIMPLE(BootSignature, formatVersion, ASN1_INTEGER),
+    ASN1_SIMPLE(BootSignature, certificate, X509),
+    ASN1_SIMPLE(BootSignature, algorithmIdentifier, X509_ALGOR),
+    ASN1_SIMPLE(BootSignature, authenticatedAttributes, AuthAttrs),
+    ASN1_SIMPLE(BootSignature, signature, ASN1_OCTET_STRING)
+} ASN1_SEQUENCE_END(BootSignature)
+
+IMPLEMENT_ASN1_FUNCTIONS(BootSignature)
+
+static BIO *g_error = NULL;
+
+/**
+ * Rounds n up to the nearest multiple of page_size
+ * @param n The value to round
+ * @param page_size Page size
+ */
+static uint64_t page_align(uint64_t n, uint64_t page_size)
+{
+    return (((n + page_size - 1) / page_size) * page_size);
+}
+
+/**
+ * Calculates the offset to the beginning of the BootSignature block
+ * based on the boot image header. The signature will start after the
+ * the boot image contents.
+ * @param fd File descriptor to the boot image
+ * @param offset Receives the offset in bytes
+ */
+static int get_signature_offset(int fd, off64_t *offset)
+{
+    int i;
+    struct boot_img_hdr hdr;
+
+    if (!offset) {
+        return -1;
+    }
+
+    if (read(fd, &hdr, sizeof(hdr)) != sizeof(hdr)) {
+        return -1;
+    }
+
+    if (memcmp(BOOT_MAGIC, hdr.magic, BOOT_MAGIC_SIZE) != 0) {
+        printf("Invalid boot image: missing magic\n");
+        return -1;
+    }
+
+    if (!hdr.page_size) {
+        printf("Invalid boot image: page size must be non-zero\n");
+        return -1;
+    }
+
+    *offset = page_align(hdr.page_size
+                    + page_align(hdr.kernel_size,  hdr.page_size)
+                    + page_align(hdr.ramdisk_size, hdr.page_size)
+                    + page_align(hdr.second_size,  hdr.page_size),
+                hdr.page_size);
+
+    return 0;
+}
+
+/**
+ * Reads and parses the ASN.1 BootSignature block from the given offset
+ * @param fd File descriptor to the boot image
+ * @param offset Offset from the beginning of file to the signature
+ * @param bs Pointer to receive the BootImage structure
+ */
+static int read_signature(int fd, off64_t offset, BootSignature **bs)
+{
+    BIO *in = NULL;
+
+    if (!bs) {
+        return -1;
+    }
+
+    if (lseek64(fd, offset, SEEK_SET) == -1) {
+        return -1;
+    }
+
+    if ((in = BIO_new_fd(fd, BIO_NOCLOSE)) == NULL) {
+        ERR_print_errors(g_error);
+        return -1;
+    }
+
+    if ((*bs = ASN1_item_d2i_bio(ASN1_ITEM_rptr(BootSignature), in, bs)) == NULL) {
+        ERR_print_errors(g_error);
+        BIO_free(in);
+        return -1;
+    }
+
+    BIO_free(in);
+    return 0;
+}
+
+/**
+ * Validates the format of the boot signature block, and checks that
+ * the length in authenticated attributes matches the actual length of
+ * the image.
+ * @param bs The boot signature block to validate
+ * @param length The actual length of the boot image without the signature
+ */
+static int validate_signature_block(const BootSignature *bs, uint64_t length)
+{
+    BIGNUM expected;
+    BIGNUM value;
+    int rc = -1;
+
+    if (!bs) {
+        return -1;
+    }
+
+    BN_init(&expected);
+    BN_init(&value);
+
+    /* Confirm that formatVersion matches our supported version */
+    if (!BN_set_word(&expected, FORMAT_VERSION)) {
+        ERR_print_errors(g_error);
+        goto vsb_done;
+    }
+
+    ASN1_INTEGER_to_BN(bs->formatVersion, &value);
+
+    if (BN_cmp(&expected, &value) != 0) {
+        printf("Unsupported signature version\n");
+        goto vsb_done;
+    }
+
+    BN_clear(&expected);
+    BN_clear(&value);
+
+    /* Confirm that the length of the image matches with the length in
+        the authenticated attributes */
+    length = htobe64(length);
+    BN_bin2bn((const unsigned char *) &length, sizeof(length), &expected);
+
+    ASN1_INTEGER_to_BN(bs->authenticatedAttributes->length, &value);
+
+    if (BN_cmp(&expected, &value) != 0) {
+        printf("Image length doesn't match signature attributes\n");
+        goto vsb_done;
+    }
+
+    rc = 0;
+
+vsb_done:
+    BN_free(&expected);
+    BN_free(&value);
+
+    return rc;
+}
+
+/**
+ * Creates a SHA-256 hash from the boot image contents and the encoded
+ * authenticated attributes.
+ * @param fd File descriptor to the boot image
+ * @param length Length of the boot image without the signature block
+ * @param aa Pointer to AuthAttrs
+ * @param digest Pointer to a buffer where the hash is written
+ */
+static int hash_image(int fd, uint64_t length, const AuthAttrs *aa,
+        unsigned char *digest)
+{
+    EVP_MD_CTX *ctx = NULL;
+    int rc = -1;
+
+    ssize_t bytes = 0;
+    unsigned char *attrs = NULL;
+    unsigned char *buffer = NULL;
+    unsigned char *p = NULL;
+    uint64_t total = 0;
+
+    if (!aa || !digest) {
+        goto hi_done;
+    }
+
+    if ((buffer = malloc(BUFFER_SIZE)) == NULL) {
+        goto hi_done;
+    }
+
+    if (lseek64(fd, 0, SEEK_SET) != 0) {
+        goto hi_done;
+    }
+
+    if ((ctx = EVP_MD_CTX_create()) == NULL) {
+        ERR_print_errors(g_error);
+        goto hi_done;
+    }
+
+    EVP_DigestInit(ctx, EVP_sha256());
+
+    do {
+        bytes = BUFFER_SIZE;
+
+        if ((length - total) < BUFFER_SIZE) {
+            bytes = length - total;
+        }
+
+        if ((bytes = read(fd, buffer, bytes)) == -1) {
+            printf("%s\n", strerror(errno));
+            goto hi_done;
+        }
+
+        EVP_DigestUpdate(ctx, buffer, bytes);
+        total += bytes;
+    } while (total < length);
+
+    if ((bytes = i2d_AuthAttrs((AuthAttrs *) aa, NULL)) < 0) {
+        ERR_print_errors(g_error);
+        goto hi_done;
+    }
+
+    if ((attrs = OPENSSL_malloc(bytes)) == NULL) {
+        ERR_print_errors(g_error);
+        goto hi_done;
+    }
+
+    p = attrs;
+
+    if (i2d_AuthAttrs((AuthAttrs *) aa, &p) < 0) {
+        ERR_print_errors(g_error);
+        goto hi_done;
+    }
+
+    EVP_DigestUpdate(ctx, attrs, bytes);
+    EVP_DigestFinal(ctx, digest, NULL);
+
+    rc = 0;
+
+hi_done:
+    if (buffer) {
+        free(buffer);
+    }
+
+    if (ctx) {
+        EVP_MD_CTX_destroy(ctx);
+    }
+
+    if (attrs) {
+        OPENSSL_free(attrs);
+    }
+
+    return rc;
+}
+
+/**
+ * Verifies the RSA signature
+ * @param fd File descriptor to the boot image
+ * @param length Length of the boot image without the signature block
+ * @param bs The boot signature block
+ */
+static int verify_signature(int fd, uint64_t length, const BootSignature *bs)
+{
+    int rc = -1;
+    EVP_PKEY *pkey = NULL;
+    RSA *rsa = NULL;
+    unsigned char digest[SHA256_DIGEST_LENGTH];
+
+    if (!bs) {
+        goto vs_done;
+    }
+
+    if (hash_image(fd, length, bs->authenticatedAttributes, digest) == -1) {
+        goto vs_done;
+    }
+
+    if ((pkey = X509_get_pubkey(bs->certificate)) == NULL) {
+        ERR_print_errors(g_error);
+        goto vs_done;
+    }
+
+    if ((rsa = EVP_PKEY_get1_RSA(pkey)) == NULL) {
+        ERR_print_errors(g_error);
+        goto vs_done;
+    }
+
+    if (!RSA_verify(NID_sha256, digest, SHA256_DIGEST_LENGTH,
+                bs->signature->data, bs->signature->length, rsa)) {
+        ERR_print_errors(g_error);
+        goto vs_done;
+    }
+
+    rc = 0;
+
+vs_done:
+    if (pkey) {
+        EVP_PKEY_free(pkey);
+    }
+
+    if (rsa) {
+        RSA_free(rsa);
+    }
+
+    return rc;
+}
+
+/**
+ * Given the file name of a signed boot image, verifies the signature
+ * @param image_file Name of the boot image file
+ */
+static int verify(const char *image_file)
+{
+    BootSignature *bs = NULL;
+    int fd = -1;
+    int rc = 1;
+    off64_t offset = 0;
+
+    if (!image_file) {
+        return rc;
+    }
+
+    if ((fd = open(image_file, O_RDONLY | O_LARGEFILE)) == -1) {
+        return rc;
+    }
+
+    if (get_signature_offset(fd, &offset) == -1) {
+        goto out;
+    }
+
+    if (read_signature(fd, offset, &bs) == -1) {
+        goto out;
+    }
+
+    if (validate_signature_block(bs, offset) == -1) {
+        goto out;
+    }
+
+    if (verify_signature(fd, offset, bs) == -1) {
+        goto out;
+    }
+
+    printf("Signature is VALID\n");
+    rc = 0;
+
+out:
+    if (bs) {
+        BootSignature_free(bs);
+    }
+
+    if (fd != -1) {
+        close(fd);
+    }
+
+    return rc;
+}
+
+static void usage()
+{
+    printf("Usage: verify_boot_signature <path-to-boot-image>\n");
+}
+
+int main(int argc, char *argv[])
+{
+    if (argc != 2) {
+        usage();
+        return 1;
+    }
+
+    /* BIO descriptor for logging OpenSSL errors to stderr */
+    if ((g_error = BIO_new_fd(STDERR_FILENO, BIO_NOCLOSE)) == NULL) {
+        printf("Failed to allocate a BIO handle for error output\n");
+        return 1;
+    }
+
+    ERR_load_crypto_strings();
+
+    return verify(argv[1]);
+}