1 files changed, 736 insertions, 0 deletions

diff --git a/src/credman.c b/src/credman.c
new file mode 100644
index 0000000..76327e5
--- /dev/null
+++ b/src/credman.c
@@ -0,0 +1,736 @@
+/*
+ * Copyright (c) 2019 Yubico AB. All rights reserved.
+ * Use of this source code is governed by a BSD-style
+ * license that can be found in the LICENSE file.
+ */
+
+#include <openssl/sha.h>
+
+#include <string.h>
+
+#include "fido.h"
+#include "fido/credman.h"
+#include "fido/es256.h"
+
+#define CMD_CRED_METADATA       0x01
+#define CMD_RP_BEGIN            0x02
+#define CMD_RP_NEXT             0x03
+#define CMD_RK_BEGIN            0x04
+#define CMD_RK_NEXT             0x05
+#define CMD_DELETE_CRED         0x06
+
+static int
+credman_grow_array(void **ptr, size_t *n_alloc, size_t *n_rx, size_t n,
+    size_t size)
+{
+        void *new_ptr;
+
+#ifdef FIDO_FUZZ
+        if (n > UINT8_MAX) {
+                fido_log_debug("%s: n > UINT8_MAX", __func__);
+                return (-1);
+        }
+#endif
+
+        if (n < *n_alloc)
+                return (0);
+
+        /* sanity check */
+        if (*n_rx > 0 || *n_rx > *n_alloc || n < *n_alloc) {
+                fido_log_debug("%s: n=%zu, n_rx=%zu, n_alloc=%zu", __func__, n,
+                    *n_rx, *n_alloc);
+                return (-1);
+        }
+
+        if ((new_ptr = recallocarray(*ptr, *n_alloc, n, size)) == NULL)
+                return (-1);
+
+        *ptr = new_ptr;
+        *n_alloc = n;
+
+        return (0);
+}
+
+static int
+credman_prepare_hmac(uint8_t cmd, const fido_blob_t *body, cbor_item_t **param,
+    fido_blob_t *hmac_data)
+{
+        cbor_item_t *param_cbor[2];
+        size_t n;
+        int ok = -1;
+
+        memset(&param_cbor, 0, sizeof(param_cbor));
+
+        if (body == NULL)
+                return (fido_blob_set(hmac_data, &cmd, sizeof(cmd)));
+
+        switch (cmd) {
+        case CMD_RK_BEGIN:
+                n = 1;
+                param_cbor[n - 1] = fido_blob_encode(body);
+                break;
+        case CMD_DELETE_CRED:
+                n = 2;
+                param_cbor[n - 1] = cbor_encode_pubkey(body);
+                break;
+        default:
+                fido_log_debug("%s: unknown cmd=0x%02x", __func__, cmd);
+                return (-1);
+        }
+
+        if (param_cbor[n - 1] == NULL) {
+                fido_log_debug("%s: cbor encode", __func__);
+                return (-1);
+        }
+        if ((*param = cbor_flatten_vector(param_cbor, n)) == NULL) {
+                fido_log_debug("%s: cbor_flatten_vector", __func__);
+                goto fail;
+        }
+        if (cbor_build_frame(cmd, param_cbor, n, hmac_data) < 0) {
+                fido_log_debug("%s: cbor_build_frame", __func__);
+                goto fail;
+        }
+
+        ok = 0;
+fail:
+        cbor_vector_free(param_cbor, nitems(param_cbor));
+
+        return (ok);
+}
+
+static int
+credman_tx(fido_dev_t *dev, uint8_t cmd, const fido_blob_t *param,
+    const char *pin)
+{
+        fido_blob_t      f;
+        fido_blob_t     *ecdh = NULL;
+        fido_blob_t      hmac;
+        es256_pk_t      *pk = NULL;
+        cbor_item_t     *argv[4];
+        int              r = FIDO_ERR_INTERNAL;
+
+        memset(&f, 0, sizeof(f));
+        memset(&hmac, 0, sizeof(hmac));
+        memset(&argv, 0, sizeof(argv));
+
+        /* subCommand */
+        if ((argv[0] = cbor_build_uint8(cmd)) == NULL) {
+                fido_log_debug("%s: cbor encode", __func__);
+                goto fail;
+        }
+
+        /* pinProtocol, pinAuth */
+        if (pin != NULL) {
+                if (credman_prepare_hmac(cmd, param, &argv[1], &hmac) < 0) {
+                        fido_log_debug("%s: credman_prepare_hmac", __func__);
+                        goto fail;
+                }
+                if ((r = fido_do_ecdh(dev, &pk, &ecdh)) != FIDO_OK) {
+                        fido_log_debug("%s: fido_do_ecdh", __func__);
+                        goto fail;
+                }
+                if ((r = cbor_add_pin_params(dev, &hmac, pk, ecdh, pin,
+                    &argv[3], &argv[2])) != FIDO_OK) {
+                        fido_log_debug("%s: cbor_add_pin_params", __func__);
+                        goto fail;
+                }
+        }
+
+        /* framing and transmission */
+        if (cbor_build_frame(CTAP_CBOR_CRED_MGMT_PRE, argv, 4, &f) < 0 ||
+            fido_tx(dev, CTAP_FRAME_INIT | CTAP_CMD_CBOR, f.ptr, f.len) < 0) {
+                fido_log_debug("%s: fido_tx", __func__);
+                r = FIDO_ERR_TX;
+                goto fail;
+        }
+
+        r = FIDO_OK;
+fail:
+        es256_pk_free(&pk);
+        fido_blob_free(&ecdh);
+        cbor_vector_free(argv, nitems(argv));
+        free(f.ptr);
+        free(hmac.ptr);
+
+        return (r);
+}
+
+static int
+credman_parse_metadata(const cbor_item_t *key, const cbor_item_t *val,
+    void *arg)
+{
+        fido_credman_metadata_t *metadata = arg;
+
+        if (cbor_isa_uint(key) == false ||
+            cbor_int_get_width(key) != CBOR_INT_8) {
+                fido_log_debug("%s: cbor type", __func__);
+                return (0); /* ignore */
+        }
+
+        switch (cbor_get_uint8(key)) {
+        case 1:
+                return (cbor_decode_uint64(val, &metadata->rk_existing));
+        case 2:
+                return (cbor_decode_uint64(val, &metadata->rk_remaining));
+        default:
+                fido_log_debug("%s: cbor type", __func__);
+                return (0); /* ignore */
+        }
+}
+
+static int
+credman_rx_metadata(fido_dev_t *dev, fido_credman_metadata_t *metadata, int ms)
+{
+        const uint8_t   cmd = CTAP_FRAME_INIT | CTAP_CMD_CBOR;
+        unsigned char   reply[512];
+        int             reply_len;
+        int             r;
+
+        memset(metadata, 0, sizeof(*metadata));
+
+        if ((reply_len = fido_rx(dev, cmd, &reply, sizeof(reply), ms)) < 0) {
+                fido_log_debug("%s: fido_rx", __func__);
+                return (FIDO_ERR_RX);
+        }
+
+        if ((r = cbor_parse_reply(reply, (size_t)reply_len, metadata,
+            credman_parse_metadata)) != FIDO_OK) {
+                fido_log_debug("%s: credman_parse_metadata", __func__);
+                return (r);
+        }
+
+        return (FIDO_OK);
+}
+
+static int
+credman_get_metadata_wait(fido_dev_t *dev, fido_credman_metadata_t *metadata,
+    const char *pin, int ms)
+{
+        int r;
+
+        if ((r = credman_tx(dev, CMD_CRED_METADATA, NULL, pin)) != FIDO_OK ||
+            (r = credman_rx_metadata(dev, metadata, ms)) != FIDO_OK)
+                return (r);
+
+        return (FIDO_OK);
+}
+
+int
+fido_credman_get_dev_metadata(fido_dev_t *dev, fido_credman_metadata_t *metadata,
+    const char *pin)
+{
+        if (fido_dev_is_fido2(dev) == false)
+                return (FIDO_ERR_INVALID_COMMAND);
+        if (pin == NULL)
+                return (FIDO_ERR_INVALID_ARGUMENT);
+
+        return (credman_get_metadata_wait(dev, metadata, pin, -1));
+}
+
+static int
+credman_parse_rk(const cbor_item_t *key, const cbor_item_t *val, void *arg)
+{
+        fido_cred_t *cred = arg;
+
+        if (cbor_isa_uint(key) == false ||
+            cbor_int_get_width(key) != CBOR_INT_8) {
+                fido_log_debug("%s: cbor type", __func__);
+                return (0); /* ignore */
+        }
+
+        switch (cbor_get_uint8(key)) {
+        case 6: /* user entity */
+                return (cbor_decode_user(val, &cred->user));
+        case 7:
+                return (cbor_decode_cred_id(val, &cred->attcred.id));
+        case 8:
+                if (cbor_decode_pubkey(val, &cred->attcred.type,
+                    &cred->attcred.pubkey) < 0)
+                        return (-1);
+                cred->type = cred->attcred.type; /* XXX */
+                return (0);
+        default:
+                fido_log_debug("%s: cbor type", __func__);
+                return (0); /* ignore */
+        }
+}
+
+static void
+credman_reset_rk(fido_credman_rk_t *rk)
+{
+        for (size_t i = 0; i < rk->n_alloc; i++) {
+                fido_cred_reset_tx(&rk->ptr[i]);
+                fido_cred_reset_rx(&rk->ptr[i]);
+        }
+
+        free(rk->ptr);
+        rk->ptr = NULL;
+        memset(rk, 0, sizeof(*rk));
+}
+
+static int
+credman_parse_rk_count(const cbor_item_t *key, const cbor_item_t *val,
+    void *arg)
+{
+        fido_credman_rk_t *rk = arg;
+        uint64_t n;
+
+        /* totalCredentials */
+        if (cbor_isa_uint(key) == false ||
+            cbor_int_get_width(key) != CBOR_INT_8 ||
+            cbor_get_uint8(key) != 9) {
+                fido_log_debug("%s: cbor_type", __func__);
+                return (0); /* ignore */
+        }
+
+        if (cbor_decode_uint64(val, &n) < 0 || n > SIZE_MAX) {
+                fido_log_debug("%s: cbor_decode_uint64", __func__);
+                return (-1);
+        }
+
+        if (credman_grow_array((void **)&rk->ptr, &rk->n_alloc, &rk->n_rx,
+            (size_t)n, sizeof(*rk->ptr)) < 0) {
+                fido_log_debug("%s: credman_grow_array", __func__);
+                return (-1);
+        }
+
+        return (0);
+}
+
+static int
+credman_rx_rk(fido_dev_t *dev, fido_credman_rk_t *rk, int ms)
+{
+        const uint8_t   cmd = CTAP_FRAME_INIT | CTAP_CMD_CBOR;
+        unsigned char   reply[2048];
+        int             reply_len;
+        int             r;
+
+        credman_reset_rk(rk);
+
+        if ((reply_len = fido_rx(dev, cmd, &reply, sizeof(reply), ms)) < 0) {
+                fido_log_debug("%s: fido_rx", __func__);
+                return (FIDO_ERR_RX);
+        }
+
+        /* adjust as needed */
+        if ((r = cbor_parse_reply(reply, (size_t)reply_len, rk,
+            credman_parse_rk_count)) != FIDO_OK) {
+                fido_log_debug("%s: credman_parse_rk_count", __func__);
+                return (r);
+        }
+
+        if (rk->n_alloc == 0) {
+                fido_log_debug("%s: n_alloc=0", __func__);
+                return (FIDO_OK);
+        }
+
+        /* parse the first rk */
+        if ((r = cbor_parse_reply(reply, (size_t)reply_len, &rk->ptr[0],
+            credman_parse_rk)) != FIDO_OK) {
+                fido_log_debug("%s: credman_parse_rk", __func__);
+                return (r);
+        }
+
+        rk->n_rx++;
+
+        return (FIDO_OK);
+}
+
+static int
+credman_rx_next_rk(fido_dev_t *dev, fido_credman_rk_t *rk, int ms)
+{
+        const uint8_t   cmd = CTAP_FRAME_INIT | CTAP_CMD_CBOR;
+        unsigned char   reply[2048];
+        int             reply_len;
+        int             r;
+
+        if ((reply_len = fido_rx(dev, cmd, &reply, sizeof(reply), ms)) < 0) {
+                fido_log_debug("%s: fido_rx", __func__);
+                return (FIDO_ERR_RX);
+        }
+
+        /* sanity check */
+        if (rk->n_rx >= rk->n_alloc) {
+                fido_log_debug("%s: n_rx=%zu, n_alloc=%zu", __func__, rk->n_rx,
+                    rk->n_alloc);
+                return (FIDO_ERR_INTERNAL);
+        }
+
+        if ((r = cbor_parse_reply(reply, (size_t)reply_len, &rk->ptr[rk->n_rx],
+            credman_parse_rk)) != FIDO_OK) {
+                fido_log_debug("%s: credman_parse_rk", __func__);
+                return (r);
+        }
+
+        return (FIDO_OK);
+}
+
+static int
+credman_get_rk_wait(fido_dev_t *dev, const char *rp_id, fido_credman_rk_t *rk,
+    const char *pin, int ms)
+{
+        fido_blob_t     rp_dgst;
+        uint8_t         dgst[SHA256_DIGEST_LENGTH];
+        int             r;
+
+        if (SHA256((const unsigned char *)rp_id, strlen(rp_id), dgst) != dgst) {
+                fido_log_debug("%s: sha256", __func__);
+                return (FIDO_ERR_INTERNAL);
+        }
+
+        rp_dgst.ptr = dgst;
+        rp_dgst.len = sizeof(dgst);
+
+        if ((r = credman_tx(dev, CMD_RK_BEGIN, &rp_dgst, pin)) != FIDO_OK ||
+            (r = credman_rx_rk(dev, rk, ms)) != FIDO_OK)
+                return (r);
+
+        while (rk->n_rx < rk->n_alloc) {
+                if ((r = credman_tx(dev, CMD_RK_NEXT, NULL, NULL)) != FIDO_OK ||
+                    (r = credman_rx_next_rk(dev, rk, ms)) != FIDO_OK)
+                        return (r);
+                rk->n_rx++;
+        }
+
+        return (FIDO_OK);
+}
+
+int
+fido_credman_get_dev_rk(fido_dev_t *dev, const char *rp_id,
+    fido_credman_rk_t *rk, const char *pin)
+{
+        if (fido_dev_is_fido2(dev) == false)
+                return (FIDO_ERR_INVALID_COMMAND);
+        if (pin == NULL)
+                return (FIDO_ERR_INVALID_ARGUMENT);
+
+        return (credman_get_rk_wait(dev, rp_id, rk, pin, -1));
+}
+
+static int
+credman_del_rk_wait(fido_dev_t *dev, const unsigned char *cred_id,
+    size_t cred_id_len, const char *pin, int ms)
+{
+        fido_blob_t cred;
+        int r;
+
+        memset(&cred, 0, sizeof(cred));
+
+        if (fido_blob_set(&cred, cred_id, cred_id_len) < 0)
+                return (FIDO_ERR_INVALID_ARGUMENT);
+
+        if ((r = credman_tx(dev, CMD_DELETE_CRED, &cred, pin)) != FIDO_OK ||
+            (r = fido_rx_cbor_status(dev, ms)) != FIDO_OK)
+                goto fail;
+
+        r = FIDO_OK;
+fail:
+        free(cred.ptr);
+
+        return (r);
+}
+
+int
+fido_credman_del_dev_rk(fido_dev_t *dev, const unsigned char *cred_id,
+    size_t cred_id_len, const char *pin)
+{
+        if (fido_dev_is_fido2(dev) == false)
+                return (FIDO_ERR_INVALID_COMMAND);
+        if (pin == NULL)
+                return (FIDO_ERR_INVALID_ARGUMENT);
+
+        return (credman_del_rk_wait(dev, cred_id, cred_id_len, pin, -1));
+}
+
+static int
+credman_parse_rp(const cbor_item_t *key, const cbor_item_t *val, void *arg)
+{
+        struct fido_credman_single_rp *rp = arg;
+
+        if (cbor_isa_uint(key) == false ||
+            cbor_int_get_width(key) != CBOR_INT_8) {
+                fido_log_debug("%s: cbor type", __func__);
+                return (0); /* ignore */
+        }
+
+        switch (cbor_get_uint8(key)) {
+        case 3:
+                return (cbor_decode_rp_entity(val, &rp->rp_entity));
+        case 4:
+                return (fido_blob_decode(val, &rp->rp_id_hash));
+        default:
+                fido_log_debug("%s: cbor type", __func__);
+                return (0); /* ignore */
+        }
+}
+
+static void
+credman_reset_rp(fido_credman_rp_t *rp)
+{
+        for (size_t i = 0; i < rp->n_alloc; i++) {
+                free(rp->ptr[i].rp_entity.id);
+                free(rp->ptr[i].rp_entity.name);
+                rp->ptr[i].rp_entity.id = NULL;
+                rp->ptr[i].rp_entity.name = NULL;
+                free(rp->ptr[i].rp_id_hash.ptr);
+                memset(&rp->ptr[i].rp_id_hash, 0,
+                    sizeof(rp->ptr[i].rp_id_hash));
+        }
+
+        free(rp->ptr);
+        rp->ptr = NULL;
+        memset(rp, 0, sizeof(*rp));
+}
+
+static int
+credman_parse_rp_count(const cbor_item_t *key, const cbor_item_t *val,
+    void *arg)
+{
+        fido_credman_rp_t *rp = arg;
+        uint64_t n;
+
+        /* totalRPs */
+        if (cbor_isa_uint(key) == false ||
+            cbor_int_get_width(key) != CBOR_INT_8 ||
+            cbor_get_uint8(key) != 5) {
+                fido_log_debug("%s: cbor_type", __func__);
+                return (0); /* ignore */
+        }
+
+        if (cbor_decode_uint64(val, &n) < 0 || n > SIZE_MAX) {
+                fido_log_debug("%s: cbor_decode_uint64", __func__);
+                return (-1);
+        }
+
+        if (credman_grow_array((void **)&rp->ptr, &rp->n_alloc, &rp->n_rx,
+            (size_t)n, sizeof(*rp->ptr)) < 0) {
+                fido_log_debug("%s: credman_grow_array", __func__);
+                return (-1);
+        }
+
+        return (0);
+}
+
+static int
+credman_rx_rp(fido_dev_t *dev, fido_credman_rp_t *rp, int ms)
+{
+        const uint8_t   cmd = CTAP_FRAME_INIT | CTAP_CMD_CBOR;
+        unsigned char   reply[2048];
+        int             reply_len;
+        int             r;
+
+        credman_reset_rp(rp);
+
+        if ((reply_len = fido_rx(dev, cmd, &reply, sizeof(reply), ms)) < 0) {
+                fido_log_debug("%s: fido_rx", __func__);
+                return (FIDO_ERR_RX);
+        }
+
+        /* adjust as needed */
+        if ((r = cbor_parse_reply(reply, (size_t)reply_len, rp,
+            credman_parse_rp_count)) != FIDO_OK) {
+                fido_log_debug("%s: credman_parse_rp_count", __func__);
+                return (r);
+        }
+
+        if (rp->n_alloc == 0) {
+                fido_log_debug("%s: n_alloc=0", __func__);
+                return (FIDO_OK);
+        }
+
+        /* parse the first rp */
+        if ((r = cbor_parse_reply(reply, (size_t)reply_len, &rp->ptr[0],
+            credman_parse_rp)) != FIDO_OK) {
+                fido_log_debug("%s: credman_parse_rp", __func__);
+                return (r);
+        }
+
+        rp->n_rx++;
+
+        return (FIDO_OK);
+}
+
+static int
+credman_rx_next_rp(fido_dev_t *dev, fido_credman_rp_t *rp, int ms)
+{
+        const uint8_t   cmd = CTAP_FRAME_INIT | CTAP_CMD_CBOR;
+        unsigned char   reply[2048];
+        int             reply_len;
+        int             r;
+
+        if ((reply_len = fido_rx(dev, cmd, &reply, sizeof(reply), ms)) < 0) {
+                fido_log_debug("%s: fido_rx", __func__);
+                return (FIDO_ERR_RX);
+        }
+
+        /* sanity check */
+        if (rp->n_rx >= rp->n_alloc) {
+                fido_log_debug("%s: n_rx=%zu, n_alloc=%zu", __func__, rp->n_rx,
+                    rp->n_alloc);
+                return (FIDO_ERR_INTERNAL);
+        }
+
+        if ((r = cbor_parse_reply(reply, (size_t)reply_len, &rp->ptr[rp->n_rx],
+            credman_parse_rp)) != FIDO_OK) {
+                fido_log_debug("%s: credman_parse_rp", __func__);
+                return (r);
+        }
+
+        return (FIDO_OK);
+}
+
+static int
+credman_get_rp_wait(fido_dev_t *dev, fido_credman_rp_t *rp, const char *pin,
+    int ms)
+{
+        int r;
+
+        if ((r = credman_tx(dev, CMD_RP_BEGIN, NULL, pin)) != FIDO_OK ||
+            (r = credman_rx_rp(dev, rp, ms)) != FIDO_OK)
+                return (r);
+
+        while (rp->n_rx < rp->n_alloc) {
+                if ((r = credman_tx(dev, CMD_RP_NEXT, NULL, NULL)) != FIDO_OK ||
+                    (r = credman_rx_next_rp(dev, rp, ms)) != FIDO_OK)
+                        return (r);
+                rp->n_rx++;
+        }
+
+        return (FIDO_OK);
+}
+
+int
+fido_credman_get_dev_rp(fido_dev_t *dev, fido_credman_rp_t *rp, const char *pin)
+{
+        if (fido_dev_is_fido2(dev) == false)
+                return (FIDO_ERR_INVALID_COMMAND);
+        if (pin == NULL)
+                return (FIDO_ERR_INVALID_ARGUMENT);
+
+        return (credman_get_rp_wait(dev, rp, pin, -1));
+}
+
+fido_credman_rk_t *
+fido_credman_rk_new(void)
+{
+        return (calloc(1, sizeof(fido_credman_rk_t)));
+}
+
+void
+fido_credman_rk_free(fido_credman_rk_t **rk_p)
+{
+        fido_credman_rk_t *rk;
+
+        if (rk_p == NULL || (rk = *rk_p) == NULL)
+                return;
+
+        credman_reset_rk(rk);
+        free(rk);
+        *rk_p = NULL;
+}
+
+size_t
+fido_credman_rk_count(const fido_credman_rk_t *rk)
+{
+        return (rk->n_rx);
+}
+
+const fido_cred_t *
+fido_credman_rk(const fido_credman_rk_t *rk, size_t idx)
+{
+        if (idx >= rk->n_alloc)
+                return (NULL);
+
+        return (&rk->ptr[idx]);
+}
+
+fido_credman_metadata_t *
+fido_credman_metadata_new(void)
+{
+        return (calloc(1, sizeof(fido_credman_metadata_t)));
+}
+
+void
+fido_credman_metadata_free(fido_credman_metadata_t **metadata_p)
+{
+        fido_credman_metadata_t *metadata;
+
+        if (metadata_p == NULL || (metadata = *metadata_p) == NULL)
+                return;
+
+        free(metadata);
+        *metadata_p = NULL;
+}
+
+uint64_t
+fido_credman_rk_existing(const fido_credman_metadata_t *metadata)
+{
+        return (metadata->rk_existing);
+}
+
+uint64_t
+fido_credman_rk_remaining(const fido_credman_metadata_t *metadata)
+{
+        return (metadata->rk_remaining);
+}
+
+fido_credman_rp_t *
+fido_credman_rp_new(void)
+{
+        return (calloc(1, sizeof(fido_credman_rp_t)));
+}
+
+void
+fido_credman_rp_free(fido_credman_rp_t **rp_p)
+{
+        fido_credman_rp_t *rp;
+
+        if (rp_p == NULL || (rp = *rp_p) == NULL)
+                return;
+
+        credman_reset_rp(rp);
+        free(rp);
+        *rp_p = NULL;
+}
+
+size_t
+fido_credman_rp_count(const fido_credman_rp_t *rp)
+{
+        return (rp->n_rx);
+}
+
+const char *
+fido_credman_rp_id(const fido_credman_rp_t *rp, size_t idx)
+{
+        if (idx >= rp->n_alloc)
+                return (NULL);
+
+        return (rp->ptr[idx].rp_entity.id);
+}
+
+const char *
+fido_credman_rp_name(const fido_credman_rp_t *rp, size_t idx)
+{
+        if (idx >= rp->n_alloc)
+                return (NULL);
+
+        return (rp->ptr[idx].rp_entity.name);
+}
+
+size_t
+fido_credman_rp_id_hash_len(const fido_credman_rp_t *rp, size_t idx)
+{
+        if (idx >= rp->n_alloc)
+                return (0);
+
+        return (rp->ptr[idx].rp_id_hash.len);
+}
+
+const unsigned char *
+fido_credman_rp_id_hash_ptr(const fido_credman_rp_t *rp, size_t idx)
+{
+        if (idx >= rp->n_alloc)
+                return (NULL);
+
+        return (rp->ptr[idx].rp_id_hash.ptr);
+}