crypto: Support DER encodings

Add encoding interfaces for DER encoding:
1. support decoding of 'bit string', 'octet string', 'object id'
and 'context specific tag' for DER encoder.
2. implemented a simple DER encoder.
3. add more testsuits for DER encoder.

Signed-off-by: lei he <helei.sig11@bytedance.com>
Message-Id: <20221008085030.70212-3-helei.sig11@bytedance.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

2 files changed, 493 insertions, 25 deletions

diff --git a/crypto/der.c b/crypto/der.c
index f877390bbb..dab3fe4f24 100644
--- a/crypto/der.c
+++ b/crypto/der.c
@@ -22,20 +22,93 @@
 #include "qemu/osdep.h"
 #include "crypto/der.h"
 
+typedef struct QCryptoDerEncodeNode {
+    uint8_t tag;
+    struct QCryptoDerEncodeNode *parent;
+    struct QCryptoDerEncodeNode *next;
+    /* for constructed type, data is null */
+    const uint8_t *data;
+    size_t dlen;
+} QCryptoDerEncodeNode;
+
+typedef struct QCryptoEncodeContext {
+    QCryptoDerEncodeNode root;
+    QCryptoDerEncodeNode *current_parent;
+    QCryptoDerEncodeNode *tail;
+} QCryptoEncodeContext;
+
 enum QCryptoDERTypeTag {
     QCRYPTO_DER_TYPE_TAG_BOOL = 0x1,
     QCRYPTO_DER_TYPE_TAG_INT = 0x2,
     QCRYPTO_DER_TYPE_TAG_BIT_STR = 0x3,
     QCRYPTO_DER_TYPE_TAG_OCT_STR = 0x4,
-    QCRYPTO_DER_TYPE_TAG_OCT_NULL = 0x5,
-    QCRYPTO_DER_TYPE_TAG_OCT_OID = 0x6,
+    QCRYPTO_DER_TYPE_TAG_NULL = 0x5,
+    QCRYPTO_DER_TYPE_TAG_OID = 0x6,
     QCRYPTO_DER_TYPE_TAG_SEQ = 0x10,
     QCRYPTO_DER_TYPE_TAG_SET = 0x11,
 };
 
-#define QCRYPTO_DER_CONSTRUCTED_MASK 0x20
+enum QCryptoDERTagClass {
+    QCRYPTO_DER_TAG_CLASS_UNIV = 0x0,
+    QCRYPTO_DER_TAG_CLASS_APPL = 0x1,
+    QCRYPTO_DER_TAG_CLASS_CONT = 0x2,
+    QCRYPTO_DER_TAG_CLASS_PRIV = 0x3,
+};
+
+enum QCryptoDERTagEnc {
+    QCRYPTO_DER_TAG_ENC_PRIM = 0x0,
+    QCRYPTO_DER_TAG_ENC_CONS = 0x1,
+};
+
+#define QCRYPTO_DER_TAG_ENC_MASK 0x20
+#define QCRYPTO_DER_TAG_ENC_SHIFT 5
+
+#define QCRYPTO_DER_TAG_CLASS_MASK 0xc0
+#define QCRYPTO_DER_TAG_CLASS_SHIFT 6
+
+#define QCRYPTO_DER_TAG_VAL_MASK 0x1f
 #define QCRYPTO_DER_SHORT_LEN_MASK 0x80
 
+#define QCRYPTO_DER_TAG(class, enc, val)           \
+    (((class) << QCRYPTO_DER_TAG_CLASS_SHIFT) |    \
+     ((enc) << QCRYPTO_DER_TAG_ENC_SHIFT) | (val))
+
+/**
+ * qcrypto_der_encode_length:
+ * @src_len: the length of source data
+ * @dst: distination to save the encoded 'length', if dst is NULL, only compute
+ * the expected buffer size in bytes.
+ * @dst_len: output parameter, indicates how many bytes wrote.
+ *
+ * Encode the 'length' part of TLV tuple.
+ */
+static void qcrypto_der_encode_length(size_t src_len,
+                                      uint8_t *dst, size_t *dst_len)
+{
+    size_t max_length = 0xFF;
+    uint8_t length_bytes = 0, header_byte;
+
+    if (src_len < QCRYPTO_DER_SHORT_LEN_MASK) {
+        header_byte = src_len;
+        *dst_len = 1;
+    } else {
+        for (length_bytes = 1; max_length < src_len; length_bytes++) {
+            max_length = (max_length << 8) + max_length;
+        }
+        header_byte = length_bytes;
+        header_byte |= QCRYPTO_DER_SHORT_LEN_MASK;
+        *dst_len = length_bytes + 1;
+    }
+    if (!dst) {
+        return;
+    }
+    *dst++ = header_byte;
+    /* Bigendian length bytes */
+    for (; length_bytes > 0; length_bytes--) {
+        *dst++ = ((src_len >> (length_bytes - 1) * 8) & 0xFF);
+    }
+}
+
 static uint8_t qcrypto_der_peek_byte(const uint8_t **data, size_t *dlen)
 {
     return **data;
@@ -150,40 +223,230 @@ static int qcrypto_der_extract_data(const uint8_t **data, size_t *dlen,
     return qcrypto_der_extract_definite_data(data, dlen, cb, ctx, errp);
 }
 
-int qcrypto_der_decode_int(const uint8_t **data, size_t *dlen,
-                           QCryptoDERDecodeCb cb, void *ctx, Error **errp)
+static int qcrypto_der_decode_tlv(const uint8_t expected_tag,
+                                  const uint8_t **data, size_t *dlen,
+                                  QCryptoDERDecodeCb cb,
+                                  void *ctx, Error **errp)
 {
+    const uint8_t *saved_data = *data;
+    size_t saved_dlen = *dlen;
     uint8_t tag;
+    int data_length;
+
     if (*dlen < 1) {
         error_setg(errp, "Need more data");
         return -1;
     }
     tag = qcrypto_der_cut_byte(data, dlen);
+    if (tag != expected_tag) {
+        error_setg(errp, "Unexpected tag: expected: %u, actual: %u",
+                   expected_tag, tag);
+        goto error;
+    }
 
-    /* INTEGER must encoded in primitive-form */
-    if (tag != QCRYPTO_DER_TYPE_TAG_INT) {
-        error_setg(errp, "Invalid integer type tag: %u", tag);
-        return -1;
+    data_length = qcrypto_der_extract_data(data, dlen, cb, ctx, errp);
+    if (data_length < 0) {
+        goto error;
     }
+    return data_length;
 
-    return qcrypto_der_extract_data(data, dlen, cb, ctx, errp);
+error:
+    *data = saved_data;
+    *dlen = saved_dlen;
+    return -1;
+}
+
+int qcrypto_der_decode_int(const uint8_t **data, size_t *dlen,
+                           QCryptoDERDecodeCb cb, void *ctx, Error **errp)
+{
+    const uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_UNIV,
+                                        QCRYPTO_DER_TAG_ENC_PRIM,
+                                        QCRYPTO_DER_TYPE_TAG_INT);
+    return qcrypto_der_decode_tlv(tag, data, dlen, cb, ctx, errp);
 }
 
 int qcrypto_der_decode_seq(const uint8_t **data, size_t *dlen,
                            QCryptoDERDecodeCb cb, void *ctx, Error **errp)
 {
-    uint8_t tag;
-    if (*dlen < 1) {
-        error_setg(errp, "Need more data");
-        return -1;
-    }
-    tag = qcrypto_der_cut_byte(data, dlen);
+    uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_UNIV,
+                                  QCRYPTO_DER_TAG_ENC_CONS,
+                                  QCRYPTO_DER_TYPE_TAG_SEQ);
+    return qcrypto_der_decode_tlv(tag, data, dlen, cb, ctx, errp);
+}
 
-    /* SEQUENCE must use constructed form */
-    if (tag != (QCRYPTO_DER_TYPE_TAG_SEQ | QCRYPTO_DER_CONSTRUCTED_MASK)) {
-        error_setg(errp, "Invalid type sequence tag: %u", tag);
-        return -1;
-    }
+int qcrypto_der_decode_octet_str(const uint8_t **data, size_t *dlen,
+                                 QCryptoDERDecodeCb cb, void *ctx, Error **errp)
+{
+    uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_UNIV,
+                                  QCRYPTO_DER_TAG_ENC_PRIM,
+                                  QCRYPTO_DER_TYPE_TAG_OCT_STR);
+    return qcrypto_der_decode_tlv(tag, data, dlen, cb, ctx, errp);
+}
+
+int qcrypto_der_decode_bit_str(const uint8_t **data, size_t *dlen,
+                               QCryptoDERDecodeCb cb, void *ctx, Error **errp)
+{
+    uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_UNIV,
+                                  QCRYPTO_DER_TAG_ENC_PRIM,
+                                  QCRYPTO_DER_TYPE_TAG_BIT_STR);
+    return qcrypto_der_decode_tlv(tag, data, dlen, cb, ctx, errp);
+}
+
+int qcrypto_der_decode_oid(const uint8_t **data, size_t *dlen,
+                           QCryptoDERDecodeCb cb, void *ctx, Error **errp)
+{
+    uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_UNIV,
+                                  QCRYPTO_DER_TAG_ENC_PRIM,
+                                  QCRYPTO_DER_TYPE_TAG_OID);
+    return qcrypto_der_decode_tlv(tag, data, dlen, cb, ctx, errp);
+}
+
+int qcrypto_der_decode_ctx_tag(const uint8_t **data, size_t *dlen, int tag_id,
+                               QCryptoDERDecodeCb cb, void *ctx, Error **errp)
+{
+    uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_CONT,
+                                  QCRYPTO_DER_TAG_ENC_CONS,
+                                  tag_id);
+    return qcrypto_der_decode_tlv(tag, data, dlen, cb, ctx, errp);
+}
 
-    return qcrypto_der_extract_data(data, dlen, cb, ctx, errp);
+static void qcrypto_der_encode_prim(QCryptoEncodeContext *ctx, uint8_t tag,
+                                    const uint8_t *data, size_t dlen)
+{
+    QCryptoDerEncodeNode *node = g_new0(QCryptoDerEncodeNode, 1);
+    size_t nbytes_len;
+
+    node->tag = tag;
+    node->data = data;
+    node->dlen = dlen;
+    node->parent = ctx->current_parent;
+
+    qcrypto_der_encode_length(dlen, NULL, &nbytes_len);
+    /* 1 byte for Tag, nbyte_len for Length, and dlen for Value */
+    node->parent->dlen += 1 + nbytes_len + dlen;
+
+    ctx->tail->next = node;
+    ctx->tail = node;
+}
+
+QCryptoEncodeContext *qcrypto_der_encode_ctx_new(void)
+{
+    QCryptoEncodeContext *ctx = g_new0(QCryptoEncodeContext, 1);
+    ctx->current_parent = &ctx->root;
+    ctx->tail = &ctx->root;
+    return ctx;
+}
+
+static void qcrypto_der_encode_cons_begin(QCryptoEncodeContext *ctx,
+                                          uint8_t tag)
+{
+    QCryptoDerEncodeNode *node = g_new0(QCryptoDerEncodeNode, 1);
+
+    node->tag = tag;
+    node->parent = ctx->current_parent;
+    ctx->current_parent = node;
+    ctx->tail->next = node;
+    ctx->tail = node;
+}
+
+static void qcrypto_der_encode_cons_end(QCryptoEncodeContext *ctx)
+{
+    QCryptoDerEncodeNode *cons_node = ctx->current_parent;
+    size_t nbytes_len;
+
+    qcrypto_der_encode_length(cons_node->dlen, NULL, &nbytes_len);
+    /* 1 byte for Tag, nbyte_len for Length, and dlen for Value */
+    cons_node->parent->dlen += 1 + nbytes_len + cons_node->dlen;
+    ctx->current_parent = cons_node->parent;
+}
+
+void qcrypto_der_encode_seq_begin(QCryptoEncodeContext *ctx)
+{
+    uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_UNIV,
+                                  QCRYPTO_DER_TAG_ENC_CONS,
+                                  QCRYPTO_DER_TYPE_TAG_SEQ);
+    qcrypto_der_encode_cons_begin(ctx, tag);
+}
+
+void qcrypto_der_encode_seq_end(QCryptoEncodeContext *ctx)
+{
+    qcrypto_der_encode_cons_end(ctx);
+}
+
+void qcrypto_der_encode_oid(QCryptoEncodeContext *ctx,
+                            const uint8_t *src, size_t src_len)
+{
+    uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_UNIV,
+                                  QCRYPTO_DER_TAG_ENC_PRIM,
+                                  QCRYPTO_DER_TYPE_TAG_OID);
+    qcrypto_der_encode_prim(ctx, tag, src, src_len);
+}
+
+void qcrypto_der_encode_int(QCryptoEncodeContext *ctx,
+                            const uint8_t *src, size_t src_len)
+{
+    uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_UNIV,
+                                  QCRYPTO_DER_TAG_ENC_PRIM,
+                                  QCRYPTO_DER_TYPE_TAG_INT);
+    qcrypto_der_encode_prim(ctx, tag, src, src_len);
+}
+
+void qcrypto_der_encode_null(QCryptoEncodeContext *ctx)
+{
+    uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_UNIV,
+                                  QCRYPTO_DER_TAG_ENC_PRIM,
+                                  QCRYPTO_DER_TYPE_TAG_NULL);
+    qcrypto_der_encode_prim(ctx, tag, NULL, 0);
+}
+
+void qcrypto_der_encode_octet_str(QCryptoEncodeContext *ctx,
+                                  const uint8_t *src, size_t src_len)
+{
+    uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_UNIV,
+                                  QCRYPTO_DER_TAG_ENC_PRIM,
+                                  QCRYPTO_DER_TYPE_TAG_OCT_STR);
+    qcrypto_der_encode_prim(ctx, tag, src, src_len);
+}
+
+void qcrypto_der_encode_octet_str_begin(QCryptoEncodeContext *ctx)
+{
+    uint8_t tag = QCRYPTO_DER_TAG(QCRYPTO_DER_TAG_CLASS_UNIV,
+                                  QCRYPTO_DER_TAG_ENC_PRIM,
+                                  QCRYPTO_DER_TYPE_TAG_OCT_STR);
+    qcrypto_der_encode_cons_begin(ctx, tag);
+}
+
+void qcrypto_der_encode_octet_str_end(QCryptoEncodeContext *ctx)
+{
+    qcrypto_der_encode_cons_end(ctx);
+}
+
+size_t qcrypto_der_encode_ctx_buffer_len(QCryptoEncodeContext *ctx)
+{
+    return ctx->root.dlen;
+}
+
+void qcrypto_der_encode_ctx_flush_and_free(QCryptoEncodeContext *ctx,
+                                           uint8_t *dst)
+{
+    QCryptoDerEncodeNode *node, *prev;
+    size_t len;
+
+    for (prev = &ctx->root;
+         (node = prev->next) && (prev->next = node->next, 1);) {
+        /* Tag */
+        *dst++ = node->tag;
+
+        /* Length */
+        qcrypto_der_encode_length(node->dlen, dst, &len);
+        dst += len;
+
+        /* Value */
+        if (node->data) {
+            memcpy(dst, node->data, node->dlen);
+            dst += node->dlen;
+        }
+        g_free(node);
+    }
+    g_free(ctx);
 }
diff --git a/crypto/der.h b/crypto/der.h
index e3d3aeacdc..0e895bbeec 100644
--- a/crypto/der.h
+++ b/crypto/der.h
@@ -22,6 +22,11 @@
 
 #include "qapi/error.h"
 
+typedef struct QCryptoEncodeContext QCryptoEncodeContext;
+
+/* rsaEncryption: 1.2.840.113549.1.1.1 */
+#define QCRYPTO_OID_rsaEncryption "\x2A\x86\x48\x86\xF7\x0D\x01\x01\x01"
+
 /* Simple decoder used to parse DER encoded rsa keys. */
 
 /**
@@ -47,14 +52,13 @@ typedef int (*QCryptoDERDecodeCb) (void *opaque, const uint8_t *value,
  * will be set to the rest length of data, if cb is not NULL, must
  * return 0 to make decode success, at last, the length of the data
  * part of the decoded INTEGER will be returned. Otherwise, -1 is
- * returned.
+ * returned and the valued of *data and *dlen keep unchanged.
  */
 int qcrypto_der_decode_int(const uint8_t **data,
                            size_t *dlen,
                            QCryptoDERDecodeCb cb,
                            void *opaque,
                            Error **errp);
-
 /**
  * qcrypto_der_decode_seq:
  *
@@ -70,7 +74,7 @@ int qcrypto_der_decode_int(const uint8_t **data,
  * will be set to the rest length of data, if cb is not NULL, must
  * return 0 to make decode success, at last, the length of the data
  * part of the decoded SEQUENCE will be returned. Otherwise, -1 is
- * returned.
+ * returned and the valued of *data and *dlen keep unchanged.
  */
 int qcrypto_der_decode_seq(const uint8_t **data,
                            size_t *dlen,
@@ -78,4 +82,205 @@ int qcrypto_der_decode_seq(const uint8_t **data,
                            void *opaque,
                            Error **errp);
 
+/**
+ * qcrypto_der_decode_oid:
+ *
+ * Decode OID from DER-encoded data, similar with der_decode_int.
+ *
+ * @data: pointer to address of input data
+ * @dlen: pointer to length of input data
+ * @cb: callback invoked when decode succeed, if cb equals NULL, no
+ * callback will be invoked
+ * @opaque: parameter passed to cb
+ *
+ * Returns: On success, *data points to rest data, and *dlen
+ * will be set to the rest length of data, if cb is not NULL, must
+ * return 0 to make decode success, at last, the length of the data
+ * part of the decoded OID will be returned. Otherwise, -1 is
+ * returned and the valued of *data and *dlen keep unchanged.
+ */
+int qcrypto_der_decode_oid(const uint8_t **data,
+                           size_t *dlen,
+                           QCryptoDERDecodeCb cb,
+                           void *opaque,
+                           Error **errp);
+
+/**
+ * qcrypto_der_decode_octet_str:
+ *
+ * Decode OCTET STRING from DER-encoded data, similar with der_decode_int.
+ *
+ * @data: pointer to address of input data
+ * @dlen: pointer to length of input data
+ * @cb: callback invoked when decode succeed, if cb equals NULL, no
+ * callback will be invoked
+ * @opaque: parameter passed to cb
+ *
+ * Returns: On success, *data points to rest data, and *dlen
+ * will be set to the rest length of data, if cb is not NULL, must
+ * return 0 to make decode success, at last, the length of the data
+ * part of the decoded OCTET STRING will be returned. Otherwise, -1 is
+ * returned and the valued of *data and *dlen keep unchanged.
+ */
+int qcrypto_der_decode_octet_str(const uint8_t **data,
+                                 size_t *dlen,
+                                 QCryptoDERDecodeCb cb,
+                                 void *opaque,
+                                 Error **errp);
+
+/**
+ * qcrypto_der_decode_bit_str:
+ *
+ * Decode BIT STRING from DER-encoded data, similar with der_decode_int.
+ *
+ * @data: pointer to address of input data
+ * @dlen: pointer to length of input data
+ * @cb: callback invoked when decode succeed, if cb equals NULL, no
+ * callback will be invoked
+ * @opaque: parameter passed to cb
+ *
+ * Returns: On success, *data points to rest data, and *dlen
+ * will be set to the rest length of data, if cb is not NULL, must
+ * return 0 to make decode success, at last, the length of the data
+ * part of the decoded BIT STRING will be returned. Otherwise, -1 is
+ * returned and the valued of *data and *dlen keep unchanged.
+ */
+int qcrypto_der_decode_bit_str(const uint8_t **data,
+                               size_t *dlen,
+                               QCryptoDERDecodeCb cb,
+                               void *opaque,
+                               Error **errp);
+
+
+/**
+ * qcrypto_der_decode_ctx_tag:
+ *
+ * Decode context specific tag
+ *
+ * @data: pointer to address of input data
+ * @dlen: pointer to length of input data
+ * @tag: expected value of context specific tag
+ * @cb: callback invoked when decode succeed, if cb equals NULL, no
+ * callback will be invoked
+ * @opaque: parameter passed to cb
+ *
+ * Returns: On success, *data points to rest data, and *dlen
+ * will be set to the rest length of data, if cb is not NULL, must
+ * return 0 to make decode success, at last, the length of the data
+ * part of the decoded BIT STRING will be returned. Otherwise, -1 is
+ * returned and the valued of *data and *dlen keep unchanged.
+ */
+int qcrypto_der_decode_ctx_tag(const uint8_t **data,
+                               size_t *dlen, int tag_id,
+                               QCryptoDERDecodeCb cb,
+                               void *opaque,
+                               Error **errp);
+
+/**
+ * qcrypto_der_encode_ctx_new:
+ *
+ * Allocate a context used for der encoding.
+ */
+QCryptoEncodeContext *qcrypto_der_encode_ctx_new(void);
+
+/**
+ * qcrypto_der_encode_seq_begin:
+ * @ctx: the encode context.
+ *
+ * Start encoding a SEQUENCE for ctx.
+ *
+ */
+void qcrypto_der_encode_seq_begin(QCryptoEncodeContext *ctx);
+
+/**
+ * qcrypto_der_encode_seq_begin:
+ * @ctx: the encode context.
+ *
+ * Finish uencoding a SEQUENCE for ctx.
+ *
+ */
+void qcrypto_der_encode_seq_end(QCryptoEncodeContext *ctx);
+
+
+/**
+ * qcrypto_der_encode_oid:
+ * @ctx: the encode context.
+ * @src: the source data of oid, note it should be already encoded, this
+ * function only add tag and length part for it.
+ *
+ * Encode an oid into ctx.
+ */
+void qcrypto_der_encode_oid(QCryptoEncodeContext *ctx,
+                            const uint8_t *src, size_t src_len);
+
+/**
+ * qcrypto_der_encode_int:
+ * @ctx: the encode context.
+ * @src: the source data of integer, note it should be already encoded, this
+ * function only add tag and length part for it.
+ *
+ * Encode an integer into ctx.
+ */
+void qcrypto_der_encode_int(QCryptoEncodeContext *ctx,
+                            const uint8_t *src, size_t src_len);
+
+/**
+ * qcrypto_der_encode_null:
+ * @ctx: the encode context.
+ *
+ * Encode a null into ctx.
+ */
+void qcrypto_der_encode_null(QCryptoEncodeContext *ctx);
+
+/**
+ * qcrypto_der_encode_octet_str:
+ * @ctx: the encode context.
+ * @src: the source data of the octet string.
+ *
+ * Encode a octet string into ctx.
+ */
+void qcrypto_der_encode_octet_str(QCryptoEncodeContext *ctx,
+                                  const uint8_t *src, size_t src_len);
+
+/**
+ * qcrypto_der_encode_octet_str_begin:
+ * @ctx: the encode context.
+ *
+ * Start encoding a octet string, All fields between
+ * qcrypto_der_encode_octet_str_begin and qcrypto_der_encode_octet_str_end
+ * are encoded as an octet string. This is useful when we need to encode a
+ * encoded SEQUNCE as OCTET STRING.
+ */
+void qcrypto_der_encode_octet_str_begin(QCryptoEncodeContext *ctx);
+
+/**
+ * qcrypto_der_encode_octet_str_end:
+ * @ctx: the encode context.
+ *
+ * Finish encoding a octet string, All fields between
+ * qcrypto_der_encode_octet_str_begin and qcrypto_der_encode_octet_str_end
+ * are encoded as an octet string. This is useful when we need to encode a
+ * encoded SEQUNCE as OCTET STRING.
+ */
+void qcrypto_der_encode_octet_str_end(QCryptoEncodeContext *ctx);
+
+/**
+ * qcrypto_der_encode_ctx_buffer_len:
+ * @ctx: the encode context.
+ *
+ * Compute the expected buffer size to save all encoded things.
+ */
+size_t qcrypto_der_encode_ctx_buffer_len(QCryptoEncodeContext *ctx);
+
+/**
+ * qcrypto_der_encode_ctx_flush_and_free:
+ * @ctx: the encode context.
+ * @dst: the distination to save the encoded data, the length of dst should
+ * not less than qcrypto_der_encode_cxt_buffer_len
+ *
+ * Flush all encoded data into dst, then free ctx.
+ */
+void qcrypto_der_encode_ctx_flush_and_free(QCryptoEncodeContext *ctx,
+                                           uint8_t *dst);
+
 #endif  /* QCRYPTO_ASN1_DECODER_H */