From 88370285cc95835c8e37e8100e783a0ec8611c03 Mon Sep 17 00:00:00 2001
From: Hayden Roche <hayden@wolfssl.com>
Date: Wed, 26 May 2021 10:26:39 -0700
Subject: [PATCH] Add an API function wc_DecryptPKCS8Key to handle decrypting a
 DER, PKCS#8 encrypted key.

---
 wolfcrypt/src/asn.c            | 61 ++++++++++++++++++++++++++--------
 wolfssl/wolfcrypt/asn_public.h |  1 +
 2 files changed, 48 insertions(+), 14 deletions(-)

diff --git a/wolfcrypt/src/asn.c b/wolfcrypt/src/asn.c
index fe20f4bc1..e322a5999 100644
--- a/wolfcrypt/src/asn.c
+++ b/wolfcrypt/src/asn.c
@@ -3921,6 +3921,48 @@ int wc_EncryptPKCS8Key(byte* key, word32 keySz, byte* out, word32 outSz,
     return ret;
 }
 
+/* PKCS#8 decryption from RFC 5208
+ *
+ * NOTE: input buffer is overwritten with decrypted data!
+ *
+ * This function takes an encrypted PKCS#8 DER key and decrypts it to PKCS#8
+ * unencrypted DER. Undoes the encryption done by wc_EncryptPKCS8Key. Returns
+ * the length of the decrypted buffer or a negative value if there was an error.
+ */
+int wc_DecryptPKCS8Key(byte* input, word32 sz, const char* password,
+        int passwordSz)
+{
+    int ret;
+    int length;
+    word32 inOutIdx = 0;
+
+    if (GetSequence(input, &inOutIdx, &length, sz) < 0) {
+        ret = ASN_PARSE_E;
+    }
+    else {
+        ret = DecryptContent(input + inOutIdx, sz - inOutIdx, password,
+                passwordSz);
+        if (ret > 0) {
+            XMEMMOVE(input, input + inOutIdx, ret);
+        }
+    }
+
+    if (ret > 0) {
+        /* DecryptContent will decrypt the data, but it will leave any padding
+         * bytes intact. This code calculates the length without the padding
+         * and we return that to the user. */
+        inOutIdx = 0;
+        if (GetSequence(input, &inOutIdx, &length, ret) < 0) {
+            ret = ASN_PARSE_E;
+        }
+        else {
+            ret = inOutIdx + length;
+        }
+    }
+
+    return ret;
+}
+
 /* Takes an unencrypted, traditional DER-encoded key and converts it to a PKCS#8
  * encrypted key. */
 int TraditionalEnc(byte* key, word32 keySz, byte* out, word32* outSz,
@@ -4146,25 +4188,16 @@ exit_dc:
     return ret;
 }
 
-
 /* Remove Encrypted PKCS8 header, move beginning of traditional to beginning
    of input */
-int ToTraditionalEnc(byte* input, word32 sz,const char* password,
+int ToTraditionalEnc(byte* input, word32 sz, const char* password,
                      int passwordSz, word32* algId)
 {
-    int ret, length;
-    word32 inOutIdx = 0;
+    int ret;
 
-    if (GetSequence(input, &inOutIdx, &length, sz) < 0) {
-        ret = ASN_PARSE_E;
-    }
-    else {
-        ret = DecryptContent(input + inOutIdx, sz - inOutIdx, password,
-                passwordSz);
-        if (ret > 0) {
-            XMEMMOVE(input, input + inOutIdx, ret);
-            ret = ToTraditional_ex(input, ret, algId);
-        }
+    ret = wc_DecryptPKCS8Key(input, sz, password, passwordSz);
+    if (ret > 0) {
+        ret = ToTraditional_ex(input, ret, algId);
     }
 
     return ret;
diff --git a/wolfssl/wolfcrypt/asn_public.h b/wolfssl/wolfcrypt/asn_public.h
index 2e539c358..289f3620e 100644
--- a/wolfssl/wolfcrypt/asn_public.h
+++ b/wolfssl/wolfcrypt/asn_public.h
@@ -585,6 +585,7 @@ WOLFSSL_API int wc_CreatePKCS8Key(byte* out, word32* outSz,
        byte* key, word32 keySz, int algoID, const byte* curveOID, word32 oidSz);
 WOLFSSL_API int wc_EncryptPKCS8Key(byte*, word32, byte*, word32, const char*,
         int, int, int, int, byte*, word32, int, WC_RNG*, void*);
+WOLFSSL_API int wc_DecryptPKCS8Key(byte*, word32, const char*, int);
 
 #ifndef NO_ASN_TIME
 /* Time */