diff --git a/scripts/maint/practracker/exceptions.txt b/scripts/maint/practracker/exceptions.txt
index 896180156b..712e59dc5b 100644
--- a/scripts/maint/practracker/exceptions.txt
+++ b/scripts/maint/practracker/exceptions.txt
@@ -121,8 +121,8 @@ problem file-size /src/core/or/policies.c 3249
 problem function-size /src/core/or/policies.c:policy_summarize() 107
 problem function-size /src/core/or/protover.c:protover_all_supported() 117
 problem file-size /src/core/or/relay.c 3173
-problem function-size /src/core/or/relay.c:circuit_receive_relay_cell() 123
-problem function-size /src/core/or/relay.c:relay_send_command_from_edge_() 112
+problem function-size /src/core/or/relay.c:circuit_receive_relay_cell() 127
+problem function-size /src/core/or/relay.c:relay_send_command_from_edge_() 116
 problem function-size /src/core/or/relay.c:connection_ap_process_end_not_open() 194
 problem function-size /src/core/or/relay.c:connection_edge_process_relay_cell_not_open() 139
 problem function-size /src/core/or/relay.c:connection_edge_process_relay_cell() 520
diff --git a/src/core/crypto/relay_crypto.c b/src/core/crypto/relay_crypto.c
index 74cccd2223..8a285131a8 100644
--- a/src/core/crypto/relay_crypto.c
+++ b/src/core/crypto/relay_crypto.c
@@ -100,12 +100,22 @@ relay_crypto_get_sendme_digest(relay_crypto_t *crypto)
   return crypto->sendme_digest;
 }
 
-/** Record the b_digest from <b>crypto</b> and put it in the sendme_digest. */
+/** Record the cell digest, indicated by is_foward_digest or not, as the
+ * SENDME cell digest. */
 void
-relay_crypto_record_sendme_digest(relay_crypto_t *crypto)
+relay_crypto_record_sendme_digest(relay_crypto_t *crypto,
+                                  bool is_foward_digest)
 {
+  struct crypto_digest_t *digest;
+
   tor_assert(crypto);
-  crypto_digest_get_digest(crypto->b_digest, (char *) crypto->sendme_digest,
+
+  digest = crypto->b_digest;
+  if (is_foward_digest) {
+    digest = crypto->f_digest;
+  }
+
+  crypto_digest_get_digest(digest, (char *) crypto->sendme_digest,
                            sizeof(crypto->sendme_digest));
 }
 
@@ -161,11 +171,6 @@ relay_decrypt_cell(circuit_t *circ, cell_t *cell,
           if (relay_digest_matches(cpath_get_incoming_digest(thishop), cell)) {
             *recognized = 1;
             *layer_hint = thishop;
-            /* This cell is for us. Keep a record of this cell because we will
-             * use it in the next SENDME cell. */
-            if (sendme_circuit_cell_is_next(thishop->deliver_window)) {
-              cpath_sendme_circuit_record_inbound_cell(thishop);
-            }
             return 0;
           }
         }
@@ -213,6 +218,9 @@ relay_encrypt_cell_outbound(cell_t *cell,
   crypt_path_t *thishop; /* counter for repeated crypts */
   cpath_set_cell_forward_digest(layer_hint, cell);
 
+  /* Record cell digest as the SENDME digest if need be. */
+  sendme_record_sending_cell_digest(TO_CIRCUIT(circ), layer_hint);
+
   thishop = layer_hint;
   /* moving from farthest to nearest hop */
   do {
@@ -237,11 +245,8 @@ relay_encrypt_cell_inbound(cell_t *cell,
 {
   relay_set_digest(or_circ->crypto.b_digest, cell);
 
-  /* We are about to send this cell outbound on the circuit. Keep a record of
-   * this cell if we are expecting that the next cell is a SENDME. */
-  if (sendme_circuit_cell_is_next(TO_CIRCUIT(or_circ)->package_window)) {
-    sendme_circuit_record_outbound_cell(or_circ);
-  }
+  /* Record cell digest as the SENDME digest if need be. */
+  sendme_record_sending_cell_digest(TO_CIRCUIT(or_circ), NULL);
 
   /* encrypt one layer */
   relay_crypt_one_payload(or_circ->crypto.b_crypto, cell->payload);
diff --git a/src/core/crypto/relay_crypto.h b/src/core/crypto/relay_crypto.h
index 7f09219c7f..9478f8d359 100644
--- a/src/core/crypto/relay_crypto.h
+++ b/src/core/crypto/relay_crypto.h
@@ -28,7 +28,10 @@ void relay_crypto_clear(relay_crypto_t *crypto);
 void relay_crypto_assert_ok(const relay_crypto_t *crypto);
 
 uint8_t *relay_crypto_get_sendme_digest(relay_crypto_t *crypto);
-void relay_crypto_record_sendme_digest(relay_crypto_t *crypto);
+
+void relay_crypto_record_sendme_digest(relay_crypto_t *crypto,
+                                       bool is_foward_digest);
+
 void
 relay_crypt_one_payload(crypto_cipher_t *cipher, uint8_t *in);
 
diff --git a/src/core/or/circuit_st.h b/src/core/or/circuit_st.h
index a68547ecb1..499bf93d6b 100644
--- a/src/core/or/circuit_st.h
+++ b/src/core/or/circuit_st.h
@@ -115,12 +115,11 @@ struct circuit_t {
    * list can not contain more than 10 digests of DIGEST_LEN bytes (20).
    *
    * At position i in the list, the digest corresponds to the
-   * ((CIRCWINDOW_INCREMENT * i) - 1)-nth cell received since we expect the
-   * (CIRCWINDOW_INCREMENT * i)-nth cell to be the SENDME and thus containing
-   * the previous cell digest.
+   * (CIRCWINDOW_INCREMENT * i)-nth cell received since we expect a SENDME to
+   * be received containing that cell digest.
    *
-   * For example, position 2 (starting at 0) means that we've received 299
-   * cells and the 299th cell digest is kept at index 2.
+   * For example, position 2 (starting at 0) means that we've received 300
+   * cells so the 300th cell digest is kept at index 2.
    *
    * At maximum, this list contains 200 bytes plus the smartlist overhead. */
   smartlist_t *sendme_last_digests;
diff --git a/src/core/or/crypt_path.c b/src/core/or/crypt_path.c
index a4b7190e21..6d5245510f 100644
--- a/src/core/or/crypt_path.c
+++ b/src/core/or/crypt_path.c
@@ -204,15 +204,6 @@ cpath_set_cell_forward_digest(crypt_path_t *cpath, cell_t *cell)
 
 /************ cpath sendme API ***************************/
 
-/** Keep the current inbound cell digest for the next SENDME digest. This part
- * is only done by the client as the circuit came back from the Exit. */
-void
-cpath_sendme_circuit_record_inbound_cell(crypt_path_t *cpath)
-{
-  tor_assert(cpath);
-  relay_crypto_record_sendme_digest(&cpath->pvt_crypto);
-}
-
 /** Return the sendme_digest of this <b>cpath</b>. */
 uint8_t *
 cpath_get_sendme_digest(crypt_path_t *cpath)
@@ -220,6 +211,15 @@ cpath_get_sendme_digest(crypt_path_t *cpath)
   return relay_crypto_get_sendme_digest(&cpath->pvt_crypto);
 }
 
+/** Record the cell digest, indicated by is_foward_digest or not, as the
+ * SENDME cell digest. */
+void
+cpath_sendme_record_cell_digest(crypt_path_t *cpath, bool is_foward_digest)
+{
+  tor_assert(cpath);
+  relay_crypto_record_sendme_digest(&cpath->pvt_crypto, is_foward_digest);
+}
+
 /************ other cpath functions ***************************/
 
 /** Return the first non-open hop in cpath, or return NULL if all
diff --git a/src/core/or/crypt_path.h b/src/core/or/crypt_path.h
index 30c14b3dce..9850610ef7 100644
--- a/src/core/or/crypt_path.h
+++ b/src/core/or/crypt_path.h
@@ -27,6 +27,9 @@ cpath_crypt_cell(const crypt_path_t *cpath, uint8_t *payload, bool is_decrypt);
 struct crypto_digest_t *
 cpath_get_incoming_digest(const crypt_path_t *cpath);
 
+void cpath_sendme_record_cell_digest(crypt_path_t *cpath,
+                                     bool is_foward_digest);
+
 void
 cpath_set_cell_forward_digest(crypt_path_t *cpath, cell_t *cell);
 
diff --git a/src/core/or/relay.c b/src/core/or/relay.c
index 066ef19dbf..5197ee6138 100644
--- a/src/core/or/relay.c
+++ b/src/core/or/relay.c
@@ -247,6 +247,10 @@ circuit_receive_relay_cell(cell_t *cell, circuit_t *circ,
   if (recognized) {
     edge_connection_t *conn = NULL;
 
+    /* Recognized cell, the cell digest has been updated, we'll record it for
+     * the SENDME if need be. */
+    sendme_record_received_cell_digest(circ, layer_hint);
+
     if (circ->purpose == CIRCUIT_PURPOSE_PATH_BIAS_TESTING) {
       if (pathbias_check_probe_response(circ, cell) == -1) {
         pathbias_count_valid_cells(circ, cell);
@@ -701,7 +705,7 @@ relay_send_command_from_edge_,(streamid_t stream_id, circuit_t *circ,
    * we need to. This call needs to be after the circuit_package_relay_cell()
    * because the cell digest is set within that function. */
   if (relay_command == RELAY_COMMAND_DATA) {
-    sendme_record_cell_digest(circ);
+    sendme_record_cell_digest_on_circ(circ, cpath_layer);
   }
 
   return 0;
diff --git a/src/core/or/sendme.c b/src/core/or/sendme.c
index 0743c48c32..7d409a16ad 100644
--- a/src/core/or/sendme.c
+++ b/src/core/or/sendme.c
@@ -25,20 +25,6 @@
 #include "lib/ctime/di_ops.h"
 #include "trunnel/sendme.h"
 
-/* The maximum supported version. Above that value, the cell can't be
- * recognized as a valid SENDME. */
-#define SENDME_MAX_SUPPORTED_VERSION 1
-
-/* The cell version constants for when emitting a cell. */
-#define SENDME_EMIT_MIN_VERSION_DEFAULT 0
-#define SENDME_EMIT_MIN_VERSION_MIN 0
-#define SENDME_EMIT_MIN_VERSION_MAX UINT8_MAX
-
-/* The cell version constants for when accepting a cell. */
-#define SENDME_ACCEPT_MIN_VERSION_DEFAULT 0
-#define SENDME_ACCEPT_MIN_VERSION_MIN 0
-#define SENDME_ACCEPT_MIN_VERSION_MAX UINT8_MAX
-
 /* Return the minimum version given by the consensus (if any) that should be
  * used when emitting a SENDME cell. */
 STATIC int
@@ -61,47 +47,53 @@ get_accept_min_version(void)
                                  SENDME_ACCEPT_MIN_VERSION_MAX);
 }
 
+/* Pop the first cell digset on the given circuit from the SENDME last digests
+ * list. NULL is returned if the list is uninitialized or empty.
+ *
+ * The caller gets ownership of the returned digest thus is responsible for
+ * freeing the memory. */
+static uint8_t *
+pop_first_cell_digest(const circuit_t *circ)
+{
+  uint8_t *circ_digest;
+
+  tor_assert(circ);
+
+  if (circ->sendme_last_digests == NULL ||
+      smartlist_len(circ->sendme_last_digests) == 0) {
+    return NULL;
+  }
+
+  /* More cell digest than the SENDME window is never suppose to happen. The
+   * cell should have been rejected before reaching this point due to its
+   * package_window down to 0 leading to a circuit close. Scream loudly but
+   * still pop the element so we don't memory leak. */
+  tor_assert_nonfatal(smartlist_len(circ->sendme_last_digests) <=
+                      CIRCWINDOW_START_MAX / CIRCWINDOW_INCREMENT);
+
+  circ_digest = smartlist_get(circ->sendme_last_digests, 0);
+  smartlist_del_keeporder(circ->sendme_last_digests, 0);
+  return circ_digest;
+}
+
 /* Return true iff the given cell digest matches the first digest in the
  * circuit sendme list. */
 static bool
-v1_digest_matches(const circuit_t *circ, const uint8_t *cell_digest)
+v1_digest_matches(const uint8_t *circ_digest, const uint8_t *cell_digest)
 {
-  bool ret = false;
-  uint8_t *circ_digest = NULL;
-
-  tor_assert(circ);
+  tor_assert(circ_digest);
   tor_assert(cell_digest);
 
-  /* We shouldn't have received a SENDME if we have no digests. Log at
-   * protocol warning because it can be tricked by sending many SENDMEs
-   * without prior data cell. */
-  if (circ->sendme_last_digests == NULL ||
-      smartlist_len(circ->sendme_last_digests) == 0) {
-    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
-           "We received a SENDME but we have no cell digests to match. "
-           "Closing circuit.");
-    goto no_match;
-  }
-
-  /* Pop the first element that was added (FIFO) and compare it. */
-  circ_digest = smartlist_get(circ->sendme_last_digests, 0);
-  smartlist_del_keeporder(circ->sendme_last_digests, 0);
-
   /* Compare the digest with the one in the SENDME. This cell is invalid
    * without a perfect match. */
   if (tor_memneq(circ_digest, cell_digest, TRUNNEL_SENDME_V1_DIGEST_LEN)) {
     log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
            "SENDME v1 cell digest do not match.");
-    goto no_match;
+    return false;
   }
-  /* Digests matches! */
-  ret = true;
 
- no_match:
-  /* This digest was popped from the circuit list. Regardless of what happens,
-   * we have no more use for it. */
-  tor_free(circ_digest);
-  return ret;
+  /* Digests matches! */
+  return true;
 }
 
 /* Return true iff the given decoded SENDME version 1 cell is valid and
@@ -111,42 +103,53 @@ v1_digest_matches(const circuit_t *circ, const uint8_t *cell_digest)
  * cell we saw which tells us that the other side has in fact seen that cell.
  * See proposal 289 for more details. */
 static bool
-cell_v1_is_valid(const sendme_cell_t *cell, const circuit_t *circ)
+cell_v1_is_valid(const sendme_cell_t *cell, const uint8_t *circ_digest)
 {
   tor_assert(cell);
-  tor_assert(circ);
+  tor_assert(circ_digest);
 
   const uint8_t *cell_digest = sendme_cell_getconstarray_data_v1_digest(cell);
-  return v1_digest_matches(circ, cell_digest);
+  return v1_digest_matches(circ_digest, cell_digest);
 }
 
 /* Return true iff the given cell version can be handled or if the minimum
  * accepted version from the consensus is known to us. */
 STATIC bool
-cell_version_is_valid(uint8_t cell_version)
+cell_version_can_be_handled(uint8_t cell_version)
 {
   int accept_version = get_accept_min_version();
 
-  /* Can we handle this version? */
+  /* We will first check if the consensus minimum accepted version can be
+   * handled by us and if not, regardless of the cell version we got, we can't
+   * continue. */
   if (accept_version > SENDME_MAX_SUPPORTED_VERSION) {
     log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
            "Unable to accept SENDME version %u (from consensus). "
-           "We only support <= %d. Probably your tor is too old?",
-           accept_version, cell_version);
+           "We only support <= %u. Probably your tor is too old?",
+           accept_version, SENDME_MAX_SUPPORTED_VERSION);
     goto invalid;
   }
 
-  /* We only accept a SENDME cell from what the consensus tells us. */
+  /* Then, is this version below the accepted version from the consensus? If
+   * yes, we must not handle it. */
   if (cell_version < accept_version) {
-    log_info(LD_PROTOCOL, "Unacceptable SENDME version %d. Only "
+    log_info(LD_PROTOCOL, "Unacceptable SENDME version %u. Only "
                           "accepting %u (from consensus). Closing circuit.",
              cell_version, accept_version);
     goto invalid;
   }
 
-  return 1;
+  /* Is this cell version supported by us? */
+  if (cell_version > SENDME_MAX_SUPPORTED_VERSION) {
+    log_info(LD_PROTOCOL, "SENDME cell version %u is not supported by us. "
+                          "We only support <= %u",
+             cell_version, SENDME_MAX_SUPPORTED_VERSION);
+    goto invalid;
+  }
+
+  return true;
  invalid:
-  return 0;
+  return false;
 }
 
 /* Return true iff the encoded SENDME cell in cell_payload of length
@@ -163,6 +166,7 @@ sendme_is_valid(const circuit_t *circ, const uint8_t *cell_payload,
                 size_t cell_payload_len)
 {
   uint8_t cell_version;
+  uint8_t *circ_digest = NULL;
   sendme_cell_t *cell = NULL;
 
   tor_assert(circ);
@@ -183,31 +187,50 @@ sendme_is_valid(const circuit_t *circ, const uint8_t *cell_payload,
   }
 
   /* Validate that we can handle this cell version. */
-  if (!cell_version_is_valid(cell_version)) {
+  if (!cell_version_can_be_handled(cell_version)) {
+    goto invalid;
+  }
+
+  /* Pop the first element that was added (FIFO). We do that regardless of the
+   * version so we don't accumulate on the circuit if v0 is used by the other
+   * end point. */
+  circ_digest = pop_first_cell_digest(circ);
+  if (circ_digest == NULL) {
+    /* We shouldn't have received a SENDME if we have no digests. Log at
+     * protocol warning because it can be tricked by sending many SENDMEs
+     * without prior data cell. */
+    log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
+           "We received a SENDME but we have no cell digests to match. "
+           "Closing circuit.");
     goto invalid;
   }
 
   /* Validate depending on the version now. */
   switch (cell_version) {
   case 0x01:
-    if (!cell_v1_is_valid(cell, circ)) {
+    if (!cell_v1_is_valid(cell, circ_digest)) {
       goto invalid;
     }
     break;
   case 0x00:
-    /* Fallthrough. Version 0, there is no work to be done on the payload so
-     * it is necessarily valid if we pass the version validation. */
+    /* Version 0, there is no work to be done on the payload so it is
+     * necessarily valid if we pass the version validation. */
+    break;
   default:
-    /* Unknown version means we can't handle it so fallback to version 0. */
+    log_warn(LD_PROTOCOL, "Unknown SENDME cell version %d received.",
+             cell_version);
+    tor_assert_nonfatal_unreached();
     break;
   }
 
   /* Valid cell. */
   sendme_cell_free(cell);
-  return 1;
+  tor_free(circ_digest);
+  return true;
  invalid:
   sendme_cell_free(cell);
-  return 0;
+  tor_free(circ_digest);
+  return false;
 }
 
 /* Build and encode a version 1 SENDME cell into payload, which must be at
@@ -274,6 +297,8 @@ send_circuit_level_sendme(circuit_t *circ, crypt_path_t *layer_hint,
   default:
     /* Unknown version, fallback to version 0 meaning no payload. */
     payload_len = 0;
+    log_debug(LD_PROTOCOL, "Emitting SENDME version 0 cell. "
+                           "Consensus emit version is %d", emit_version);
     break;
   }
 
@@ -287,34 +312,54 @@ send_circuit_level_sendme(circuit_t *circ, crypt_path_t *layer_hint,
   return 0;
 }
 
+/* Record the cell digest only if the next cell is expected to be a SENDME. */
+static void
+record_cell_digest_on_circ(circuit_t *circ, const uint8_t *sendme_digest)
+{
+  tor_assert(circ);
+  tor_assert(sendme_digest);
+
+  /* Add the digest to the last seen list in the circuit. */
+  if (circ->sendme_last_digests == NULL) {
+    circ->sendme_last_digests = smartlist_new();
+  }
+  smartlist_add(circ->sendme_last_digests,
+                tor_memdup(sendme_digest, DIGEST_LEN));
+}
+
 /*
  * Public API
  */
 
-/** Keep the current inbound cell digest for the next SENDME digest. This part
- * is only done by the client as the circuit came back from the Exit. */
-void
-sendme_circuit_record_outbound_cell(or_circuit_t *or_circ)
-{
-  tor_assert(or_circ);
-  relay_crypto_record_sendme_digest(&or_circ->crypto);
-}
-
 /** Return true iff the next cell for the given cell window is expected to be
  * a SENDME.
  *
  * We are able to know that because the package or deliver window value minus
  * one cell (the possible SENDME cell) should be a multiple of the increment
  * window value. */
-bool
-sendme_circuit_cell_is_next(int window)
+static bool
+circuit_sendme_cell_is_next(int window)
 {
-  /* Is this the last cell before a SENDME? The idea is that if the package or
-   * deliver window reaches a multiple of the increment, after this cell, we
-   * should expect a SENDME. */
+  /* At the start of the window, no SENDME will be expected. */
+  if (window == CIRCWINDOW_START) {
+    return false;
+  }
+
+  /* Are we at the limit of the increment and if not, we don't expect next
+   * cell is a SENDME.
+   *
+   * We test against the window minus 1 because when we are looking if the
+   * next cell is a SENDME, the window (either package or deliver) hasn't been
+   * decremented just yet so when this is called, we are currently processing
+   * the "window - 1" cell.
+   *
+   * This function is used when recording a cell digest and this is done quite
+   * low in the stack when decrypting or encrypting a cell. The window is only
+   * updated once the cell is actually put in the outbuf. */
   if (((window - 1) % CIRCWINDOW_INCREMENT) != 0) {
     return false;
   }
+
   /* Next cell is expected to be a SENDME. */
   return true;
 }
@@ -372,6 +417,7 @@ sendme_connection_edge_consider_sending(edge_connection_t *conn)
 void
 sendme_circuit_consider_sending(circuit_t *circ, crypt_path_t *layer_hint)
 {
+  bool sent_one_sendme = false;
   const uint8_t *digest;
 
   while ((layer_hint ? layer_hint->deliver_window : circ->deliver_window) <=
@@ -387,6 +433,12 @@ sendme_circuit_consider_sending(circuit_t *circ, crypt_path_t *layer_hint)
     if (send_circuit_level_sendme(circ, layer_hint, digest) < 0) {
       return; /* The circuit's closed, don't continue */
     }
+    /* Current implementation is not suppose to send multiple SENDME at once
+     * because this means we would use the same relay crypto digest for each
+     * SENDME leading to a mismatch on the other side and the circuit to
+     * collapse. Scream loudly if it ever happens so we can address it. */
+    tor_assert_nonfatal(!sent_one_sendme);
+    sent_one_sendme = true;
   }
 }
 
@@ -409,6 +461,12 @@ sendme_process_circuit_level(crypt_path_t *layer_hint,
   tor_assert(circ);
   tor_assert(cell_payload);
 
+  /* Validate the SENDME cell. Depending on the version, different validation
+   * can be done. An invalid SENDME requires us to close the circuit. */
+  if (!sendme_is_valid(circ, cell_payload, cell_payload_len)) {
+    return -END_CIRC_REASON_TORPROTOCOL;
+  }
+
   /* If we are the origin of the circuit, we are the Client so we use the
    * layer hint (the Exit hop) for the package window tracking. */
   if (CIRCUIT_IS_ORIGIN(circ)) {
@@ -433,13 +491,6 @@ sendme_process_circuit_level(crypt_path_t *layer_hint,
      * are rate limited. */
     circuit_read_valid_data(TO_ORIGIN_CIRCUIT(circ), cell_payload_len);
   } else {
-    /* Validate the SENDME cell. Depending on the version, different
-     * validation can be done. An invalid SENDME requires us to close the
-     * circuit. It is only done if we are the Exit of the circuit. */
-    if (!sendme_is_valid(circ, cell_payload, cell_payload_len)) {
-      return -END_CIRC_REASON_TORPROTOCOL;
-    }
-
     /* We aren't the origin of this circuit so we are the Exit and thus we
      * track the package window with the circuit object. */
     if ((circ->package_window + CIRCWINDOW_INCREMENT) >
@@ -568,34 +619,90 @@ int
 sendme_note_stream_data_packaged(edge_connection_t *conn)
 {
   tor_assert(conn);
-  return --conn->package_window;
+  log_debug(LD_APP, "Stream package_window now %d.", --conn->package_window);
+  return conn->package_window;
 }
 
-/* Note the cell digest in the circuit sendme last digests FIFO if applicable.
- * It is safe to pass a circuit that isn't meant to track those digests. */
+/* Record the cell digest into the circuit sendme digest list depending on
+ * which edge we are. The digest is recorded only if we expect the next cell
+ * that we will receive is a SENDME so we can match the digest. */
 void
-sendme_record_cell_digest(circuit_t *circ)
+sendme_record_cell_digest_on_circ(circuit_t *circ, crypt_path_t *cpath)
 {
-  const uint8_t *digest;
+  int package_window;
+  uint8_t *sendme_digest;
 
   tor_assert(circ);
 
-  /* We only keep the cell digest if we are the Exit on that circuit and if
-   * this cell is the last one before the client should send a SENDME. */
-  if (CIRCUIT_IS_ORIGIN(circ)) {
-    return;
+  package_window = circ->package_window;
+  if (cpath) {
+    package_window = cpath->package_window;
   }
+
   /* Is this the last cell before a SENDME? The idea is that if the
    * package_window reaches a multiple of the increment, after this cell, we
    * should expect a SENDME. */
-  if (!sendme_circuit_cell_is_next(circ->package_window)) {
+  if (!circuit_sendme_cell_is_next(package_window)) {
     return;
   }
 
-  /* Add the digest to the last seen list in the circuit. */
-  digest = relay_crypto_get_sendme_digest(&TO_OR_CIRCUIT(circ)->crypto);
-  if (circ->sendme_last_digests == NULL) {
-    circ->sendme_last_digests = smartlist_new();
+  /* Getting the digest is expensive so we only do it once we are certain to
+   * record it on the circuit. */
+  if (cpath) {
+    sendme_digest = cpath_get_sendme_digest(cpath);
+  } else {
+    sendme_digest =
+      relay_crypto_get_sendme_digest(&TO_OR_CIRCUIT(circ)->crypto);
   }
-  smartlist_add(circ->sendme_last_digests, tor_memdup(digest, DIGEST_LEN));
+
+  record_cell_digest_on_circ(circ, sendme_digest);
+}
+
+/* Called once we decrypted a cell and recognized it. Record the cell digest
+ * as the next sendme digest only if the next cell we'll send on the circuit
+ * is expected to be a SENDME. */
+void
+sendme_record_received_cell_digest(circuit_t *circ, crypt_path_t *cpath)
+{
+  tor_assert(circ);
+
+  /* Only record if the next cell is expected to be a SENDME. */
+  if (!circuit_sendme_cell_is_next(cpath ? cpath->deliver_window :
+                                           circ->deliver_window)) {
+    return;
+  }
+
+  if (cpath) {
+    /* Record incoming digest. */
+    cpath_sendme_record_cell_digest(cpath, false);
+  } else {
+    /* Record foward digest. */
+    relay_crypto_record_sendme_digest(&TO_OR_CIRCUIT(circ)->crypto, true);
+  }
+}
+
+/* Called once we encrypted a cell. Record the cell digest as the next sendme
+ * digest only if the next cell we expect to receive is a SENDME so we can
+ * match the digests. */
+void
+sendme_record_sending_cell_digest(circuit_t *circ, crypt_path_t *cpath)
+{
+  tor_assert(circ);
+
+  /* Only record if the next cell is expected to be a SENDME. */
+  if (!circuit_sendme_cell_is_next(cpath ? cpath->package_window :
+                                           circ->package_window)) {
+    goto end;
+  }
+
+  if (cpath) {
+    /* Record the forward digest. */
+    cpath_sendme_record_cell_digest(cpath, true);
+  } else {
+    /* Record the incoming digest. */
+    relay_crypto_record_sendme_digest(&TO_OR_CIRCUIT(circ)->crypto, false);
+  }
+
+ end:
+  return;
 }
diff --git a/src/core/or/sendme.h b/src/core/or/sendme.h
index ac18bbdd31..cdbdf55ac7 100644
--- a/src/core/or/sendme.h
+++ b/src/core/or/sendme.h
@@ -34,16 +34,29 @@ int sendme_note_circuit_data_packaged(circuit_t *circ,
                                       crypt_path_t *layer_hint);
 int sendme_note_stream_data_packaged(edge_connection_t *conn);
 
-/* Track cell digest. */
-void sendme_record_cell_digest(circuit_t *circ);
-void sendme_circuit_record_outbound_cell(or_circuit_t *or_circ);
-
-/* Circuit level information. */
-bool sendme_circuit_cell_is_next(int window);
+/* Record cell digest on circuit. */
+void sendme_record_cell_digest_on_circ(circuit_t *circ, crypt_path_t *cpath);
+/* Record cell digest as the SENDME digest. */
+void sendme_record_received_cell_digest(circuit_t *circ, crypt_path_t *cpath);
+void sendme_record_sending_cell_digest(circuit_t *circ, crypt_path_t *cpath);
 
 /* Private section starts. */
 #ifdef SENDME_PRIVATE
 
+/* The maximum supported version. Above that value, the cell can't be
+ * recognized as a valid SENDME. */
+#define SENDME_MAX_SUPPORTED_VERSION 1
+
+/* The cell version constants for when emitting a cell. */
+#define SENDME_EMIT_MIN_VERSION_DEFAULT 0
+#define SENDME_EMIT_MIN_VERSION_MIN 0
+#define SENDME_EMIT_MIN_VERSION_MAX UINT8_MAX
+
+/* The cell version constants for when accepting a cell. */
+#define SENDME_ACCEPT_MIN_VERSION_DEFAULT 0
+#define SENDME_ACCEPT_MIN_VERSION_MIN 0
+#define SENDME_ACCEPT_MIN_VERSION_MAX UINT8_MAX
+
 /*
  * Unit tests declaractions.
  */
@@ -52,7 +65,7 @@ bool sendme_circuit_cell_is_next(int window);
 STATIC int get_emit_min_version(void);
 STATIC int get_accept_min_version(void);
 
-STATIC bool cell_version_is_valid(uint8_t cell_version);
+STATIC bool cell_version_can_be_handled(uint8_t cell_version);
 
 STATIC ssize_t build_cell_payload_v1(const uint8_t *cell_digest,
                                      uint8_t *payload);
diff --git a/src/test/test_relaycell.c b/src/test/test_relaycell.c
index 0623583511..c65279fb25 100644
--- a/src/test/test_relaycell.c
+++ b/src/test/test_relaycell.c
@@ -17,6 +17,7 @@
 #include "core/or/circuitbuild.h"
 #include "core/or/circuitlist.h"
 #include "core/or/connection_edge.h"
+#include "core/or/sendme.h"
 #include "core/or/relay.h"
 #include "test/test.h"
 #include "test/log_test_helpers.h"
@@ -812,7 +813,11 @@ test_circbw_relay(void *arg)
   ASSERT_UNCOUNTED_BW();
 
   /* Sendme on circuit with non-full window: counted */
-  PACK_CELL(0, RELAY_COMMAND_SENDME, "Data1234");
+  PACK_CELL(0, RELAY_COMMAND_SENDME, "");
+  /* Recording a cell, the window is updated after decryption so off by one in
+   * order to record and then we process it with the proper window. */
+  circ->cpath->package_window = 901;
+  sendme_record_cell_digest_on_circ(TO_CIRCUIT(circ), circ->cpath);
   circ->cpath->package_window = 900;
   connection_edge_process_relay_cell(&cell, TO_CIRCUIT(circ), edgeconn,
                                      circ->cpath);
diff --git a/src/test/test_sendme.c b/src/test/test_sendme.c
index d40fbaf862..fa5ae115ac 100644
--- a/src/test/test_sendme.c
+++ b/src/test/test_sendme.c
@@ -46,26 +46,12 @@ static void
 test_v1_record_digest(void *arg)
 {
   or_circuit_t *or_circ = NULL;
-  origin_circuit_t *orig_circ = NULL;
   circuit_t *circ = NULL;
 
   (void) arg;
 
-  /* Create our dummy circuits. */
-  orig_circ = origin_circuit_new();
-  tt_assert(orig_circ);
+  /* Create our dummy circuit. */
   or_circ = or_circuit_new(1, NULL);
-
-  /* Start by pointing to the origin circuit. */
-  circ = TO_CIRCUIT(orig_circ);
-  circ->purpose = CIRCUIT_PURPOSE_S_REND_JOINED;
-
-  /* We should never note SENDME digest on origin circuit. */
-  sendme_record_cell_digest(circ);
-  tt_assert(!circ->sendme_last_digests);
-  /* We do not need the origin circuit for now. */
-  orig_circ = NULL;
-  circuit_free_(circ);
   /* Points it to the OR circuit now. */
   circ = TO_CIRCUIT(or_circ);
 
@@ -73,23 +59,23 @@ test_v1_record_digest(void *arg)
    * in order to catched the CIRCWINDOW_INCREMENT-nth cell. Try something that
    * shouldn't be noted. */
   circ->package_window = CIRCWINDOW_INCREMENT;
-  sendme_record_cell_digest(circ);
+  sendme_record_cell_digest_on_circ(circ, NULL);
   tt_assert(!circ->sendme_last_digests);
 
   /* This should work now. Package window at CIRCWINDOW_INCREMENT + 1. */
   circ->package_window++;
-  sendme_record_cell_digest(circ);
+  sendme_record_cell_digest_on_circ(circ, NULL);
   tt_assert(circ->sendme_last_digests);
   tt_int_op(smartlist_len(circ->sendme_last_digests), OP_EQ, 1);
 
   /* Next cell in the package window shouldn't do anything. */
   circ->package_window++;
-  sendme_record_cell_digest(circ);
+  sendme_record_cell_digest_on_circ(circ, NULL);
   tt_int_op(smartlist_len(circ->sendme_last_digests), OP_EQ, 1);
 
   /* The next CIRCWINDOW_INCREMENT should add one more digest. */
   circ->package_window = (CIRCWINDOW_INCREMENT * 2) + 1;
-  sendme_record_cell_digest(circ);
+  sendme_record_cell_digest_on_circ(circ, NULL);
   tt_int_op(smartlist_len(circ->sendme_last_digests), OP_EQ, 2);
 
  done:
@@ -136,9 +122,9 @@ test_v1_consensus_params(void *arg)
   smartlist_add(current_md_consensus->net_params,
                 (void *) "sendme_accept_min_version=1");
   /* Minimum acceptable value is 1. */
-  tt_int_op(cell_version_is_valid(1), OP_EQ, true);
+  tt_int_op(cell_version_can_be_handled(1), OP_EQ, true);
   /* Minimum acceptable value is 1 so a cell version of 0 is refused. */
-  tt_int_op(cell_version_is_valid(0), OP_EQ, false);
+  tt_int_op(cell_version_can_be_handled(0), OP_EQ, false);
 
  done:
   free_mock_consensus();
@@ -157,11 +143,13 @@ test_v1_build_cell(void *arg)
 
   or_circ = or_circuit_new(1, NULL);
   circ = TO_CIRCUIT(or_circ);
+  circ->sendme_last_digests = smartlist_new();
 
   cell_digest = crypto_digest_new();
   tt_assert(cell_digest);
   crypto_digest_add_bytes(cell_digest, "AAAAAAAAAAAAAAAAAAAA", 20);
   crypto_digest_get_digest(cell_digest, (char *) digest, sizeof(digest));
+  smartlist_add(circ->sendme_last_digests, tor_memdup(digest, sizeof(digest)));
 
   /* SENDME v1 payload is 3 bytes + 20 bytes digest. See spec. */
   ret = build_cell_payload_v1(digest, payload);
@@ -171,6 +159,8 @@ test_v1_build_cell(void *arg)
 
   /* An empty payload means SENDME version 0 thus valid. */
   tt_int_op(sendme_is_valid(circ, payload, 0), OP_EQ, true);
+  /* Current phoney digest should have been popped. */
+  tt_int_op(smartlist_len(circ->sendme_last_digests), OP_EQ, 0);
 
   /* An unparseable cell means invalid. */
   setup_full_capture_of_logs(LOG_INFO);
@@ -188,7 +178,7 @@ test_v1_build_cell(void *arg)
 
   /* Note the wrong digest in the circuit, cell should fail validation. */
   circ->package_window = CIRCWINDOW_INCREMENT + 1;
-  sendme_record_cell_digest(circ);
+  sendme_record_cell_digest_on_circ(circ, NULL);
   tt_int_op(smartlist_len(circ->sendme_last_digests), OP_EQ, 1);
   setup_full_capture_of_logs(LOG_INFO);
   tt_int_op(sendme_is_valid(circ, payload, sizeof(payload)), OP_EQ, false);
@@ -200,7 +190,7 @@ test_v1_build_cell(void *arg)
   /* Record the cell digest into the circuit, cell should validate. */
   memcpy(or_circ->crypto.sendme_digest, digest, sizeof(digest));
   circ->package_window = CIRCWINDOW_INCREMENT + 1;
-  sendme_record_cell_digest(circ);
+  sendme_record_cell_digest_on_circ(circ, NULL);
   tt_int_op(smartlist_len(circ->sendme_last_digests), OP_EQ, 1);
   tt_int_op(sendme_is_valid(circ, payload, sizeof(payload)), OP_EQ, true);
   /* After a validation, the last digests is always popped out. */
@@ -253,6 +243,33 @@ test_cell_payload_pad(void *arg)
   ;
 }
 
+static void
+test_cell_version_validation(void *arg)
+{
+  (void) arg;
+
+  /* We currently only support up to SENDME_MAX_SUPPORTED_VERSION so we are
+   * going to test the boundaries there. */
+
+  tt_assert(cell_version_can_be_handled(SENDME_MAX_SUPPORTED_VERSION));
+
+  /* Version below our supported should pass. */
+  tt_assert(cell_version_can_be_handled(SENDME_MAX_SUPPORTED_VERSION - 1));
+
+  /* Extra version from our supported should fail. */
+  tt_assert(!cell_version_can_be_handled(SENDME_MAX_SUPPORTED_VERSION + 1));
+
+  /* Simple check for version 0. */
+  tt_assert(cell_version_can_be_handled(0));
+
+  /* We MUST handle the default cell version that we emit or accept. */
+  tt_assert(cell_version_can_be_handled(SENDME_EMIT_MIN_VERSION_DEFAULT));
+  tt_assert(cell_version_can_be_handled(SENDME_ACCEPT_MIN_VERSION_DEFAULT));
+
+ done:
+  ;
+}
+
 struct testcase_t sendme_tests[] = {
   { "v1_record_digest", test_v1_record_digest, TT_FORK,
     NULL, NULL },
@@ -262,6 +279,8 @@ struct testcase_t sendme_tests[] = {
     NULL, NULL },
   { "cell_payload_pad", test_cell_payload_pad, TT_FORK,
     NULL, NULL },
+  { "cell_version_validation", test_cell_version_validation, TT_FORK,
+    NULL, NULL },
 
   END_OF_TESTCASES
 };