crypto/cms: add CAdES-BES signed attributes validation

for signing certificate V2 and signing certificate extensions.

CAdES: lowercase name for now internal methods.

crypto/cms: generated file changes.

Add some CHANGES entries.

[extended tests]

Reviewed-by: Shane Lontis <shane.lontis@oracle.com>
Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/8098)

10 files changed, 296 insertions, 114 deletions

diff --git a/crypto/cms/cms_err.c b/crypto/cms/cms_err.c
index 526d77357e..16e25afc7f 100644
--- a/crypto/cms/cms_err.c
+++ b/crypto/cms/cms_err.c
@@ -52,6 +52,10 @@ static const ERR_STRING_DATA CMS_str_reasons[] = {
     {ERR_PACK(ERR_LIB_CMS, 0, CMS_R_ERROR_SETTING_KEY), "error setting key"},
     {ERR_PACK(ERR_LIB_CMS, 0, CMS_R_ERROR_SETTING_RECIPIENTINFO),
     "error setting recipientinfo"},
+    {ERR_PACK(ERR_LIB_CMS, 0, CMS_R_ESS_NO_SIGNING_CERTID_ATTRIBUTE),
+    "ess no signing certid attribute"},
+    {ERR_PACK(ERR_LIB_CMS, 0, CMS_R_ESS_SIGNING_CERTID_MISMATCH_ERROR),
+    "ess signing certid mismatch error"},
     {ERR_PACK(ERR_LIB_CMS, 0, CMS_R_INVALID_ENCRYPTED_KEY_LENGTH),
     "invalid encrypted key length"},
     {ERR_PACK(ERR_LIB_CMS, 0, CMS_R_INVALID_KEY_ENCRYPTION_PARAMETER),
diff --git a/crypto/cms/cms_ess.c b/crypto/cms/cms_ess.c
index 3901074033..e3604f7db8 100644
--- a/crypto/cms/cms_ess.c
+++ b/crypto/cms/cms_ess.c
@@ -21,6 +21,9 @@
 
 DEFINE_STACK_OF(GENERAL_NAMES)
 DEFINE_STACK_OF(CMS_SignerInfo)
+DEFINE_STACK_OF(ESS_CERT_ID)
+DEFINE_STACK_OF(ESS_CERT_ID_V2)
+DEFINE_STACK_OF(X509)
 
 IMPLEMENT_ASN1_FUNCTIONS(CMS_ReceiptRequest)
 
@@ -29,33 +32,100 @@ IMPLEMENT_ASN1_FUNCTIONS(CMS_ReceiptRequest)
 int CMS_get1_ReceiptRequest(CMS_SignerInfo *si, CMS_ReceiptRequest **prr)
 {
     ASN1_STRING *str;
-    CMS_ReceiptRequest *rr = NULL;
-    if (prr)
+    CMS_ReceiptRequest *rr;
+    ASN1_OBJECT *obj = OBJ_nid2obj(NID_id_smime_aa_receiptRequest);
+
+    if (prr != NULL)
         *prr = NULL;
-    str = CMS_signed_get0_data_by_OBJ(si,
-                                      OBJ_nid2obj
-                                      (NID_id_smime_aa_receiptRequest), -3,
-                                      V_ASN1_SEQUENCE);
-    if (!str)
+    str = CMS_signed_get0_data_by_OBJ(si, obj, -3, V_ASN1_SEQUENCE);
+    if (str == NULL)
         return 0;
 
     rr = ASN1_item_unpack(str, ASN1_ITEM_rptr(CMS_ReceiptRequest));
-    if (!rr)
+    if (rr == NULL)
         return -1;
-    if (prr)
+    if (prr != NULL)
         *prr = rr;
     else
         CMS_ReceiptRequest_free(rr);
     return 1;
 }
 
+/*
+    First, get the ESS_SIGNING_CERT(V2) signed attribute from |si|.
+    Then check matching of each cert of trust |chain| with one of 
+    the |cert_ids|(Hash+IssuerID) list from this ESS_SIGNING_CERT.
+    Derived from ts_check_signing_certs()
+*/
+int ess_check_signing_certs(CMS_SignerInfo *si, STACK_OF(X509) *chain)
+{
+    ESS_SIGNING_CERT *ss = NULL;
+    ESS_SIGNING_CERT_V2 *ssv2 = NULL;
+    X509 *cert;
+    int i = 0, ret = 0;
+
+    if (cms_signerinfo_get_signing_cert(si, &ss) > 0 && ss->cert_ids != NULL) {
+        STACK_OF(ESS_CERT_ID) *cert_ids = ss->cert_ids;
+
+        cert = sk_X509_value(chain, 0);
+        if (ess_find_cert(cert_ids, cert) != 0)
+            goto err;
+
+        /*
+         * Check the other certificates of the chain.
+         * Fail if no signing certificate ids found for each certificate.
+         */
+        if (sk_ESS_CERT_ID_num(cert_ids) > 1) {
+            /* for each chain cert, try to find its cert id */
+            for (i = 1; i < sk_X509_num(chain); ++i) {
+                cert = sk_X509_value(chain, i);
+                if (ess_find_cert(cert_ids, cert) < 0)
+                    goto err;
+            }
+        }
+    } else if (cms_signerinfo_get_signing_cert_v2(si, &ssv2) > 0
+                   && ssv2->cert_ids!= NULL) {
+        STACK_OF(ESS_CERT_ID_V2) *cert_ids_v2 = ssv2->cert_ids;
+
+        cert = sk_X509_value(chain, 0);
+        if (ess_find_cert_v2(cert_ids_v2, cert) != 0)
+            goto err;
+
+        /*
+         * Check the other certificates of the chain.
+         * Fail if no signing certificate ids found for each certificate.
+         */
+        if (sk_ESS_CERT_ID_V2_num(cert_ids_v2) > 1) {
+            /* for each chain cert, try to find its cert id */
+            for (i = 1; i < sk_X509_num(chain); ++i) {
+                cert = sk_X509_value(chain, i);
+                if (ess_find_cert_v2(cert_ids_v2, cert) < 0)
+                    goto err;
+            }
+        }
+    } else {
+        CMSerr(CMS_F_ESS_CHECK_SIGNING_CERTS,
+               CMS_R_ESS_NO_SIGNING_CERTID_ATTRIBUTE);
+        return 0;
+    }
+    ret = 1;
+ err:
+    if (!ret)
+        CMSerr(CMS_F_ESS_CHECK_SIGNING_CERTS,
+               CMS_R_ESS_SIGNING_CERTID_MISMATCH_ERROR);
+
+    ESS_SIGNING_CERT_free(ss);
+    ESS_SIGNING_CERT_V2_free(ssv2);
+    return ret;
+}
+
 CMS_ReceiptRequest *CMS_ReceiptRequest_create0(unsigned char *id, int idlen,
                                                int allorfirst,
                                                STACK_OF(GENERAL_NAMES)
                                                *receiptList, STACK_OF(GENERAL_NAMES)
                                                *receiptsTo)
 {
-    CMS_ReceiptRequest *rr = NULL;
+    CMS_ReceiptRequest *rr;
 
     rr = CMS_ReceiptRequest_new();
     if (rr == NULL)
@@ -145,6 +215,7 @@ static int cms_msgSigDigest(CMS_SignerInfo *si,
                             unsigned char *dig, unsigned int *diglen)
 {
     const EVP_MD *md;
+
     md = EVP_get_digestbyobj(si->digestAlgorithm->algorithm);
     if (md == NULL)
         return 0;
@@ -160,6 +231,7 @@ int cms_msgSigDigest_add1(CMS_SignerInfo *dest, CMS_SignerInfo *src)
 {
     unsigned char dig[EVP_MAX_MD_SIZE];
     unsigned int diglen;
+
     if (!cms_msgSigDigest(src, dig, &diglen)) {
         CMSerr(CMS_F_CMS_MSGSIGDIGEST_ADD1, CMS_R_MSGSIGDIGEST_ERROR);
         return 0;
diff --git a/crypto/cms/cms_local.h b/crypto/cms/cms_local.h
index 00ea9006c8..68c885622b 100644
--- a/crypto/cms/cms_local.h
+++ b/crypto/cms/cms_local.h
@@ -421,6 +421,9 @@ int cms_RecipientInfo_pwri_crypt(const CMS_ContentInfo *cms, CMS_RecipientInfo *
 /* SignerInfo routines */
 int CMS_si_check_attributes(const CMS_SignerInfo *si);
 
+/* ESS routines */
+int ess_check_signing_certs(CMS_SignerInfo *si, STACK_OF(X509) *chain);
+
 DECLARE_ASN1_ITEM(CMS_CertificateChoices)
 DECLARE_ASN1_ITEM(CMS_DigestedData)
 DECLARE_ASN1_ITEM(CMS_EncryptedData)
diff --git a/crypto/cms/cms_smime.c b/crypto/cms/cms_smime.c
index dbdc815e97..a83edce0f7 100644
--- a/crypto/cms/cms_smime.c
+++ b/crypto/cms/cms_smime.c
@@ -233,7 +233,8 @@ CMS_ContentInfo *CMS_EncryptedData_encrypt(BIO *in, const EVP_CIPHER *cipher,
 static int cms_signerinfo_verify_cert(CMS_SignerInfo *si,
                                       X509_STORE *store,
                                       STACK_OF(X509) *certs,
-                                      STACK_OF(X509_CRL) *crls)
+                                      STACK_OF(X509_CRL) *crls,
+                                      STACK_OF(X509) **chain)
 {
     X509_STORE_CTX *ctx = X509_STORE_CTX_new();
     X509 *signer;
@@ -262,6 +263,10 @@ static int cms_signerinfo_verify_cert(CMS_SignerInfo *si,
         goto err;
     }
     r = 1;
+
+    /* also send back the trust chain when required */
+    if (chain != NULL)
+        *chain = X509_STORE_CTX_get1_chain(ctx);
  err:
     X509_STORE_CTX_free(ctx);
     return r;
@@ -275,9 +280,11 @@ int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs,
     STACK_OF(CMS_SignerInfo) *sinfos;
     STACK_OF(X509) *cms_certs = NULL;
     STACK_OF(X509_CRL) *crls = NULL;
+    STACK_OF(X509) **si_chains = NULL;
     X509 *signer;
     int i, scount = 0, ret = 0;
     BIO *cmsbio = NULL, *tmpin = NULL, *tmpout = NULL;
+    int cadesVerify = (flags & CMS_CADES) != 0;
 
     if (!dcont && !check_content(cms))
         return 0;
@@ -312,27 +319,44 @@ int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs,
     }
 
     /* Attempt to verify all signers certs */
-
-    if (!(flags & CMS_NO_SIGNER_CERT_VERIFY)) {
+    /* at this point scount == sk_CMS_SignerInfo_num(sinfos) */
+
+    if ((flags & CMS_NO_SIGNER_CERT_VERIFY) == 0 || cadesVerify) {
+        if (cadesVerify) {
+            /* Certificate trust chain is required to check CAdES signature */
+            si_chains = OPENSSL_zalloc(scount * sizeof(si_chains[0]));
+            if (si_chains == NULL) {
+                CMSerr(CMS_F_CMS_VERIFY, ERR_R_MALLOC_FAILURE);
+                goto err;
+            }
+        }
         cms_certs = CMS_get1_certs(cms);
         if (!(flags & CMS_NOCRL))
             crls = CMS_get1_crls(cms);
-        for (i = 0; i < sk_CMS_SignerInfo_num(sinfos); i++) {
+        for (i = 0; i < scount; i++) {
             si = sk_CMS_SignerInfo_value(sinfos, i);
-            if (!cms_signerinfo_verify_cert(si, store, cms_certs, crls))
+
+            if (!cms_signerinfo_verify_cert(si, store, cms_certs, crls,
+                                            si_chains ? &si_chains[i] : NULL))
                 goto err;
         }
     }
 
     /* Attempt to verify all SignerInfo signed attribute signatures */
 
-    if (!(flags & CMS_NO_ATTR_VERIFY)) {
-        for (i = 0; i < sk_CMS_SignerInfo_num(sinfos); i++) {
+    if ((flags & CMS_NO_ATTR_VERIFY) == 0 || cadesVerify) {
+        for (i = 0; i < scount; i++) {
             si = sk_CMS_SignerInfo_value(sinfos, i);
             if (CMS_signed_get_attr_count(si) < 0)
                 continue;
             if (CMS_SignerInfo_verify(si) <= 0)
                 goto err;
+            if (cadesVerify) {
+                STACK_OF(X509) *si_chain = si_chains ? si_chains[i] : NULL;
+
+                if (ess_check_signing_certs(si, si_chain) <= 0)
+                    goto err;
+            }
         }
     }
 
@@ -420,6 +444,11 @@ int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs,
         BIO_free_all(tmpout);
 
  err2:
+    if (si_chains != NULL) {
+        for (i = 0; i < scount; ++i)
+            sk_X509_pop_free(si_chains[i], X509_free);
+        OPENSSL_free(si_chains);
+    }
     sk_X509_pop_free(cms_certs, X509_free);
     sk_X509_CRL_pop_free(crls, X509_CRL_free);
 
diff --git a/crypto/err/openssl.txt b/crypto/err/openssl.txt
index 1b2c94b0a2..8afc67e747 100644
--- a/crypto/err/openssl.txt
+++ b/crypto/err/openssl.txt
@@ -320,6 +320,7 @@ CMS_F_CMS_SET_DETACHED:147:CMS_set_detached
 CMS_F_CMS_SIGN:148:CMS_sign
 CMS_F_CMS_SIGNED_DATA_INIT:149:cms_signed_data_init
 CMS_F_CMS_SIGNERINFO_CONTENT_SIGN:150:cms_SignerInfo_content_sign
+CMS_F_CMS_SIGNERINFO_GET_CHAIN:184:cms_signerinfo_get_chain
 CMS_F_CMS_SIGNERINFO_SIGN:151:CMS_SignerInfo_sign
 CMS_F_CMS_SIGNERINFO_VERIFY:152:CMS_SignerInfo_verify
 CMS_F_CMS_SIGNERINFO_VERIFY_CERT:153:cms_signerinfo_verify_cert
@@ -329,6 +330,7 @@ CMS_F_CMS_SI_CHECK_ATTRIBUTES:183:CMS_si_check_attributes
 CMS_F_CMS_STREAM:155:CMS_stream
 CMS_F_CMS_UNCOMPRESS:156:CMS_uncompress
 CMS_F_CMS_VERIFY:157:CMS_verify
+CMS_F_ESS_CHECK_SIGNING_CERTS:185:ess_check_signing_certs
 CMS_F_KEK_UNWRAP_KEY:180:kek_unwrap_key
 COMP_F_BIO_ZLIB_FLUSH:99:bio_zlib_flush
 COMP_F_BIO_ZLIB_NEW:100:bio_zlib_new
@@ -2188,6 +2190,8 @@ CMS_R_ERROR_READING_MESSAGEDIGEST_ATTRIBUTE:114:\
 	error reading messagedigest attribute
 CMS_R_ERROR_SETTING_KEY:115:error setting key
 CMS_R_ERROR_SETTING_RECIPIENTINFO:116:error setting recipientinfo
+CMS_R_ESS_NO_SIGNING_CERTID_ATTRIBUTE:182:ess no signing certid attribute
+CMS_R_ESS_SIGNING_CERTID_MISMATCH_ERROR:183:ess signing certid mismatch error
 CMS_R_INVALID_ENCRYPTED_KEY_LENGTH:117:invalid encrypted key length
 CMS_R_INVALID_KEY_ENCRYPTION_PARAMETER:176:invalid key encryption parameter
 CMS_R_INVALID_KEY_LENGTH:118:invalid key length
diff --git a/crypto/ess/build.info b/crypto/ess/build.info
index 24fcecc8f5..fa2bc41d08 100644
--- a/crypto/ess/build.info
+++ b/crypto/ess/build.info
@@ -1,3 +1,8 @@
 LIBS=../../libcrypto
-SOURCE[../../libcrypto]= \
-        ess_lib.c ess_asn1.c ess_err.c
+
+IF[{- !$disabled{'cms'} and !$disabled{'ts'} -}]
+  SOURCE[../../libcrypto]= ess_lib.c
+ENDIF
+
+SOURCE[../../libcrypto]= ess_asn1.c ess_err.c 
+
diff --git a/crypto/ess/ess_asn1.c b/crypto/ess/ess_asn1.c
index 19589d97f3..a8d13a3a20 100644
--- a/crypto/ess/ess_asn1.c
+++ b/crypto/ess/ess_asn1.c
@@ -1,5 +1,5 @@
 /*
- * Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 2019-2020 The OpenSSL Project Authors. All Rights Reserved.
  *
  * Licensed under the Apache License 2.0 (the "License").  You may not use
  * this file except in compliance with the License.  You can obtain a copy
@@ -9,9 +9,11 @@
 
 #include <openssl/err.h>
 #include <openssl/asn1t.h>
+#include <openssl/cms.h>
 #include <openssl/ess.h>
 #include <openssl/x509v3.h>
 #include "crypto/ess.h"
+#include "crypto/cms.h"
 
 /* ASN1 stuff for ESS Structure */
 
@@ -55,3 +57,61 @@ ASN1_SEQUENCE(ESS_SIGNING_CERT_V2) = {
 
 IMPLEMENT_ASN1_FUNCTIONS(ESS_SIGNING_CERT_V2)
 IMPLEMENT_ASN1_DUP_FUNCTION(ESS_SIGNING_CERT_V2)
+
+/* No cms support means no CMS_SignerInfo* definitions */
+#ifndef OPENSSL_NO_CMS
+
+/*
+ * Returns < 0 if attribute is not found, 1 if found, or 
+ * -1 on attribute parsing failure.
+ */
+int cms_signerinfo_get_signing_cert_v2(CMS_SignerInfo *si,
+                                       ESS_SIGNING_CERT_V2 **psc)
+{
+    ASN1_STRING *str;
+    ESS_SIGNING_CERT_V2 *sc;
+    ASN1_OBJECT *obj = OBJ_nid2obj(NID_id_smime_aa_signingCertificateV2);
+
+    if (psc != NULL)
+        *psc = NULL;
+    str = CMS_signed_get0_data_by_OBJ(si, obj, -3, V_ASN1_SEQUENCE);
+    if (str == NULL)
+        return 0;
+
+    sc = ASN1_item_unpack(str, ASN1_ITEM_rptr(ESS_SIGNING_CERT_V2));
+    if (sc == NULL)
+        return -1;
+    if (psc != NULL)
+        *psc = sc;
+    else
+        ESS_SIGNING_CERT_V2_free(sc);
+    return 1;
+}
+
+/*
+ * Returns < 0 if attribute is not found, 1 if found, or 
+ * -1 on attribute parsing failure.
+ */
+int cms_signerinfo_get_signing_cert(CMS_SignerInfo *si,
+                                    ESS_SIGNING_CERT **psc)
+{
+    ASN1_STRING *str;
+    ESS_SIGNING_CERT *sc;
+    ASN1_OBJECT *obj = OBJ_nid2obj(NID_id_smime_aa_signingCertificate);
+
+    if (psc != NULL)
+        *psc = NULL;
+    str = CMS_signed_get0_data_by_OBJ(si, obj, -3, V_ASN1_SEQUENCE);
+    if (str == NULL)
+        return 0;
+
+    sc = ASN1_item_unpack(str, ASN1_ITEM_rptr(ESS_SIGNING_CERT));
+    if (sc == NULL)
+        return -1;
+    if (psc != NULL)
+        *psc = sc;
+    else
+        ESS_SIGNING_CERT_free(sc);
+    return 1;
+}
+#endif  /* !OPENSSL_NO_CMS */
diff --git a/crypto/ess/ess_err.c b/crypto/ess/ess_err.c
index b494aa246f..6547645fea 100644
--- a/crypto/ess/ess_err.c
+++ b/crypto/ess/ess_err.c
@@ -1,6 +1,6 @@
 /*
  * Generated by util/mkerr.pl DO NOT EDIT
- * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
  *
  * Licensed under the Apache License 2.0 (the "License").  You may not use
  * this file except in compliance with the License.  You can obtain a copy
diff --git a/crypto/ess/ess_lib.c b/crypto/ess/ess_lib.c
index 9d9defa9d7..17f9db98ff 100644
--- a/crypto/ess/ess_lib.c
+++ b/crypto/ess/ess_lib.c
@@ -15,8 +15,8 @@
 
 DEFINE_STACK_OF(ESS_CERT_ID)
 DEFINE_STACK_OF(ESS_CERT_ID_V2)
-DEFINE_STACK_OF(X509)
 DEFINE_STACK_OF(GENERAL_NAME)
+DEFINE_STACK_OF(X509)
 
 static ESS_CERT_ID *ESS_CERT_ID_new_init(X509 *cert, int issuer_needed);
 static ESS_CERT_ID_V2 *ESS_CERT_ID_V2_new_init(const EVP_MD *hash_alg,
@@ -61,9 +61,12 @@ static ESS_CERT_ID *ESS_CERT_ID_new_init(X509 *cert, int issuer_needed)
     unsigned char cert_sha1[SHA_DIGEST_LENGTH];
 
     /* Call for side-effect of computing hash and caching extensions */
-    X509_check_purpose(cert, -1, 0);
+    if (!X509v3_cache_extensions(cert, NULL, NULL))
+        return NULL;
+
     if ((cid = ESS_CERT_ID_new()) == NULL)
         goto err;
+    /* TODO(3.0): fetch sha1 algorithm from providers */
     if (!X509_digest(cert, EVP_sha1(), cert_sha1, NULL))
         goto err;
     if (!ASN1_OCTET_STRING_set(cid->hash, cert_sha1, SHA_DIGEST_LENGTH))
@@ -85,8 +88,8 @@ static ESS_CERT_ID *ESS_CERT_ID_new_init(X509 *cert, int issuer_needed)
         goto err;
     name = NULL;            /* Ownership is lost. */
     ASN1_INTEGER_free(cid->issuer_serial->serial);
-    if (!(cid->issuer_serial->serial =
-          ASN1_INTEGER_dup(X509_get_serialNumber(cert))))
+    if ((cid->issuer_serial->serial =
+          ASN1_INTEGER_dup(X509_get_serialNumber(cert))) == NULL)
         goto err;
 
     return cid;
@@ -159,6 +162,7 @@ static ESS_CERT_ID_V2 *ESS_CERT_ID_V2_new_init(const EVP_MD *hash_alg,
         cid->hash_alg = NULL;
     }
 
+    /* TODO(3.0): fetch sha1 algorithm from providers */
     if (!X509_digest(cert, hash_alg, hash, &hash_len))
         goto err;
 
@@ -196,8 +200,9 @@ ESS_SIGNING_CERT *ESS_SIGNING_CERT_get(PKCS7_SIGNER_INFO *si)
 {
     ASN1_TYPE *attr;
     const unsigned char *p;
+
     attr = PKCS7_get_signed_attribute(si, NID_id_smime_aa_signingCertificate);
-    if (!attr)
+    if (attr == NULL)
         return NULL;
     p = attr->value.sequence->data;
     return d2i_ESS_SIGNING_CERT(NULL, &p, attr->value.sequence->length);
@@ -273,3 +278,86 @@ int ESS_SIGNING_CERT_V2_add(PKCS7_SIGNER_INFO *si,
     OPENSSL_free(pp);
     return 0;
 }
+
+static int ess_issuer_serial_cmp(const ESS_ISSUER_SERIAL *is, const X509 *cert)
+{
+    GENERAL_NAME *issuer;
+
+    if (is == NULL || cert == NULL || sk_GENERAL_NAME_num(is->issuer) != 1)
+        return -1;
+
+    issuer = sk_GENERAL_NAME_value(is->issuer, 0);
+    if (issuer->type != GEN_DIRNAME
+        || X509_NAME_cmp(issuer->d.dirn, X509_get_issuer_name(cert)) != 0)
+        return -1;
+
+    return ASN1_INTEGER_cmp(is->serial, X509_get0_serialNumber(cert));
+}
+
+/* Returns < 0 if certificate is not found, certificate index otherwise. */
+int ess_find_cert(const STACK_OF(ESS_CERT_ID) *cert_ids, X509 *cert)
+{
+    int i;
+    unsigned char cert_sha1[SHA_DIGEST_LENGTH];
+
+    if (cert_ids == NULL || cert == NULL)
+        return -1;
+
+    /* Recompute SHA1 hash of certificate if necessary (side effect). */
+    if (!X509v3_cache_extensions(cert, NULL, NULL))
+        return -1;
+
+    /* TODO(3.0): fetch sha1 algorithm from providers */
+    if (!X509_digest(cert, EVP_sha1(), cert_sha1, NULL))
+        return -1;
+
+    /* Look for cert in the cert_ids vector. */
+    for (i = 0; i < sk_ESS_CERT_ID_num(cert_ids); ++i) {
+        const ESS_CERT_ID *cid = sk_ESS_CERT_ID_value(cert_ids, i);
+
+        if (cid->hash->length == SHA_DIGEST_LENGTH
+            && memcmp(cid->hash->data, cert_sha1, SHA_DIGEST_LENGTH) == 0) {
+            const ESS_ISSUER_SERIAL *is = cid->issuer_serial;
+
+            if (is == NULL || ess_issuer_serial_cmp(is, cert) == 0)
+                return i;
+        }
+    }
+
+    return -1;
+}
+
+/* Returns < 0 if certificate is not found, certificate index otherwise. */
+int ess_find_cert_v2(const STACK_OF(ESS_CERT_ID_V2) *cert_ids, const X509 *cert)
+{
+    int i;
+    unsigned char cert_digest[EVP_MAX_MD_SIZE];
+    unsigned int len;
+
+    /* Look for cert in the cert_ids vector. */
+    for (i = 0; i < sk_ESS_CERT_ID_V2_num(cert_ids); ++i) {
+        const ESS_CERT_ID_V2 *cid = sk_ESS_CERT_ID_V2_value(cert_ids, i);
+        const EVP_MD *md;
+
+        if (cid != NULL && cid->hash_alg != NULL)
+            md = EVP_get_digestbyobj(cid->hash_alg->algorithm);
+        else
+            md = EVP_sha256();
+
+        /* TODO(3.0): fetch sha1 algorithm from providers */
+        if (!X509_digest(cert, md, cert_digest, &len))
+            return -1;
+
+        if (cid->hash->length != (int)len)
+            return -1;
+
+        if (memcmp(cid->hash->data, cert_digest, cid->hash->length) == 0) {
+            const ESS_ISSUER_SERIAL *is = cid->issuer_serial;
+
+            if (is == NULL || ess_issuer_serial_cmp(is, cert) == 0)
+                return i;
+        }
+    }
+
+    return -1;
+}
diff --git a/crypto/ts/ts_rsp_verify.c b/crypto/ts/ts_rsp_verify.c
index b872f75bea..c909b211d4 100644
--- a/crypto/ts/ts_rsp_verify.c
+++ b/crypto/ts/ts_rsp_verify.c
@@ -26,8 +26,7 @@ static int ts_verify_cert(X509_STORE *store, STACK_OF(X509) *untrusted,
                           X509 *signer, STACK_OF(X509) **chain);
 static int ts_check_signing_certs(PKCS7_SIGNER_INFO *si,
                                   STACK_OF(X509) *chain);
-static int ts_find_cert(STACK_OF(ESS_CERT_ID) *cert_ids, X509 *cert);
-static int ts_issuer_serial_cmp(ESS_ISSUER_SERIAL *is, X509 *cert);
+
 static int int_ts_RESP_verify_token(TS_VERIFY_CTX *ctx,
                                     PKCS7 *token, TS_TST_INFO *tst_info);
 static int ts_check_status_info(TS_RESP *response);
@@ -44,7 +43,6 @@ static int ts_check_nonces(const ASN1_INTEGER *a, TS_TST_INFO *tst_info);
 static int ts_check_signer_name(GENERAL_NAME *tsa_name, X509 *signer);
 static int ts_find_name(STACK_OF(GENERAL_NAME) *gen_names,
                         GENERAL_NAME *name);
-static int ts_find_cert_v2(STACK_OF(ESS_CERT_ID_V2) *cert_ids, X509 *cert);
 
 /*
  * This must be large enough to hold all values in ts_status_text (with
@@ -218,7 +216,7 @@ static int ts_check_signing_certs(PKCS7_SIGNER_INFO *si,
     if (ss != NULL) {
         cert_ids = ss->cert_ids;
         cert = sk_X509_value(chain, 0);
-        if (ts_find_cert(cert_ids, cert) != 0)
+        if (ess_find_cert(cert_ids, cert) != 0)
             goto err;
 
         /*
@@ -228,14 +226,14 @@ static int ts_check_signing_certs(PKCS7_SIGNER_INFO *si,
         if (sk_ESS_CERT_ID_num(cert_ids) > 1) {
             for (i = 1; i < sk_X509_num(chain); ++i) {
                 cert = sk_X509_value(chain, i);
-                if (ts_find_cert(cert_ids, cert) < 0)
+                if (ess_find_cert(cert_ids, cert) < 0)
                     goto err;
             }
         }
     } else if (ssv2 != NULL) {
         cert_ids_v2 = ssv2->cert_ids;
         cert = sk_X509_value(chain, 0);
-        if (ts_find_cert_v2(cert_ids_v2, cert) != 0)
+        if (ess_find_cert_v2(cert_ids_v2, cert) != 0)
             goto err;
 
         /*
@@ -245,7 +243,7 @@ static int ts_check_signing_certs(PKCS7_SIGNER_INFO *si,
         if (sk_ESS_CERT_ID_V2_num(cert_ids_v2) > 1) {
             for (i = 1; i < sk_X509_num(chain); ++i) {
                 cert = sk_X509_value(chain, i);
-                if (ts_find_cert_v2(cert_ids_v2, cert) < 0)
+                if (ess_find_cert_v2(cert_ids_v2, cert) < 0)
                     goto err;
             }
         }
@@ -263,87 +261,6 @@ static int ts_check_signing_certs(PKCS7_SIGNER_INFO *si,
     return ret;
 }
 
-/* Returns < 0 if certificate is not found, certificate index otherwise. */
-static int ts_find_cert(STACK_OF(ESS_CERT_ID) *cert_ids, X509 *cert)
-{
-    int i;
-    unsigned char cert_sha1[SHA_DIGEST_LENGTH];
-
-    if (!cert_ids || !cert)
-        return -1;
-
-    /* Recompute SHA1 hash of certificate if necessary (side effect). */
-    X509_check_purpose(cert, -1, 0);
-
-    if (!X509_digest(cert, EVP_sha1(), cert_sha1, NULL))
-        return -1;
-
-    /* Look for cert in the cert_ids vector. */
-    for (i = 0; i < sk_ESS_CERT_ID_num(cert_ids); ++i) {
-        ESS_CERT_ID *cid = sk_ESS_CERT_ID_value(cert_ids, i);
-
-        if (cid->hash->length == SHA_DIGEST_LENGTH
-            && memcmp(cid->hash->data, cert_sha1, SHA_DIGEST_LENGTH) == 0) {
-            ESS_ISSUER_SERIAL *is = cid->issuer_serial;
-            if (!is || !ts_issuer_serial_cmp(is, cert))
-                return i;
-        }
-    }
-
-    return -1;
-}
-
-/* Returns < 0 if certificate is not found, certificate index otherwise. */
-static int ts_find_cert_v2(STACK_OF(ESS_CERT_ID_V2) *cert_ids, X509 *cert)
-{
-    int i;
-    unsigned char cert_digest[EVP_MAX_MD_SIZE];
-    unsigned int len;
-
-    /* Look for cert in the cert_ids vector. */
-    for (i = 0; i < sk_ESS_CERT_ID_V2_num(cert_ids); ++i) {
-        ESS_CERT_ID_V2 *cid = sk_ESS_CERT_ID_V2_value(cert_ids, i);
-        const EVP_MD *md;
-
-        if (cid->hash_alg != NULL)
-            md = EVP_get_digestbyobj(cid->hash_alg->algorithm);
-        else
-            md = EVP_sha256();
-
-        if (!X509_digest(cert, md, cert_digest, &len))
-            return -1;
-        if (cid->hash->length != (int)len)
-            return -1;
-
-        if (memcmp(cid->hash->data, cert_digest, cid->hash->length) == 0) {
-            ESS_ISSUER_SERIAL *is = cid->issuer_serial;
-
-            if (is == NULL || !ts_issuer_serial_cmp(is, cert))
-                return i;
-        }
-    }
-
-    return -1;
-}
-
-static int ts_issuer_serial_cmp(ESS_ISSUER_SERIAL *is, X509 *cert)
-{
-    GENERAL_NAME *issuer;
-
-    if (!is || !cert || sk_GENERAL_NAME_num(is->issuer) != 1)
-        return -1;
-
-    issuer = sk_GENERAL_NAME_value(is->issuer, 0);
-    if (issuer->type != GEN_DIRNAME
-        || X509_NAME_cmp(issuer->d.dirn, X509_get_issuer_name(cert)))
-        return -1;
-
-    if (ASN1_INTEGER_cmp(is->serial, X509_get_serialNumber(cert)))
-        return -1;
-
-    return 0;
-}
-
 /*-
  * Verifies whether 'response' contains a valid response with regards
  * to the settings of the context: