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diff --git a/crypto/der.h b/crypto/der.h
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+/*
+ * Copyright (c) 2022 Bytedance
+ * Author: lei he <helei.sig11@bytedance.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef QCRYPTO_ASN1_DECODER_H
+#define QCRYPTO_ASN1_DECODER_H
+
+#include "qapi/error.h"
+
+/* Simple decoder used to parse DER encoded rsa keys. */
+
+/**
+ *  @opaque: user context.
+ *  @value: the starting address of |value| part of 'Tag-Length-Value' pattern.
+ *  @vlen: length of the |value|.
+ *  Returns: 0 for success, any other value is considered an error.
+ */
+typedef int (*QCryptoDERDecodeCb) (void *opaque, const uint8_t *value,
+                                   size_t vlen, Error **errp);
+
+/**
+ * qcrypto_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
+ *
+ * Decode integer from DER-encoded data.
+ *
+ * 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 INTEGER will be returned. Otherwise, -1 is
+ * returned.
+ */
+int qcrypto_der_decode_int(const uint8_t **data,
+                           size_t *dlen,
+                           QCryptoDERDecodeCb cb,
+                           void *opaque,
+                           Error **errp);
+
+/**
+ * qcrypto_der_decode_seq:
+ *
+ * Decode sequence 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 SEQUENCE will be returned. Otherwise, -1 is
+ * returned.
+ */
+int qcrypto_der_decode_seq(const uint8_t **data,
+                           size_t *dlen,
+                           QCryptoDERDecodeCb cb,
+                           void *opaque,
+                           Error **errp);
+
+#endif  /* QCRYPTO_ASN1_DECODER_H */