From eb4b9d8c992896586e5c390fffa1fddf82249316 Mon Sep 17 00:00:00 2001
From: Jens Steube <jens.steube@gmail.com>
Date: Thu, 18 Nov 2021 11:41:55 +0100
Subject: [PATCH] Electrum Wallet: Added new entropy-based check to test
 whether the decryption was successful or not

---
 OpenCL/m21800-pure.cl | 50 +++++++++++++++++++++++++++++++++++++------
 docs/changes.txt      |  1 +
 2 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/OpenCL/m21800-pure.cl b/OpenCL/m21800-pure.cl
index 6de91529b..0fa671837 100644
--- a/OpenCL/m21800-pure.cl
+++ b/OpenCL/m21800-pure.cl
@@ -35,6 +35,9 @@ typedef struct electrum_tmp
 
 } electrum_tmp_t;
 
+#define MIN_ENTROPY 3.0
+#define MAX_ENTROPY 6.0
+
 DECLSPEC void hmac_sha512_run_V (u32x *w0, u32x *w1, u32x *w2, u32x *w3, u32x *w4, u32x *w5, u32x *w6, u32x *w7, u64x *ipad, u64x *opad, u64x *digest)
 {
   digest[0] = ipad[0];
@@ -489,8 +492,8 @@ KERNEL_FQ void m21800_comp (KERN_ATTR_TMPS_ESALT (electrum_tmp_t, electrum_t))
 
   // #define AES_LEN 1024
   // in my tests it also worked with only 128 input bytes !
-  #define AES_LEN       128
-  #define AES_LEN_DIV_4  32
+  #define AES_LEN       1024
+  #define AES_LEN_DIV_4  256
 
   u32 buf_full[AES_LEN_DIV_4];
 
@@ -513,7 +516,11 @@ KERNEL_FQ void m21800_comp (KERN_ATTR_TMPS_ESALT (electrum_tmp_t, electrum_t))
 
   // early reject
 
-  if ((buf[0] & 0x0006ffff) != 0x00049c78) return; // allow 0b100 or 0b101 at the end of 3rd byte
+  // changed: 17.11.2021
+  // I had not cracked some sample Salt Type 5 wallets with known passwords provided by the owner.
+  // It was necessary to remove this early rejection and add a new signature
+  // The decrypted data was this: {"seed_version": ...
+  //if ((buf[0] & 0x0006ffff) != 0x00049c78) return; // allow 0b100 or 0b101 at the end of 3rd byte
 
   buf[1] ^= iv[1];
   buf[2] ^= iv[2];
@@ -556,7 +563,6 @@ KERNEL_FQ void m21800_comp (KERN_ATTR_TMPS_ESALT (electrum_tmp_t, electrum_t))
     buf_full[j + 3] = buf[3];
   }
 
-
   /*
    * zlib inflate/decompress:
    */
@@ -572,9 +578,9 @@ KERNEL_FQ void m21800_comp (KERN_ATTR_TMPS_ESALT (electrum_tmp_t, electrum_t))
 
   // output:
 
-  #define OUT_SIZE 16
+  #define OUT_SIZE 1024
 
-  u8 tmp[OUT_SIZE];
+  u8 tmp[OUT_SIZE] = { 0 };
 
   infstream.avail_out = OUT_SIZE;
   infstream.next_out  = tmp;
@@ -593,6 +599,38 @@ KERNEL_FQ void m21800_comp (KERN_ATTR_TMPS_ESALT (electrum_tmp_t, electrum_t))
     return;
   }
 
+  /*
+   * Check with some strange signature.
+   * The main problem is that the (invalid) decrypted data processed by zlib often results in random patterns but with low entropy,
+   * so that a simple entropy check is not sufficient
+   */
+
+  if (tmp[0] == '{')
+  {
+    int qcnt = 0;
+    int ccnt = 0;
+
+    for (int i = 1; i < 1024; i++)
+    {
+      if (tmp[i] == '"') qcnt++;
+      if (tmp[i] == ':') ccnt++;
+    }
+
+    if ((qcnt >= 3) && (ccnt >= 3))
+    {
+      const float entropy = hc_get_entropy ((const u32 *) tmp, 256);
+
+      if ((entropy >= MIN_ENTROPY) && (entropy <= MAX_ENTROPY))
+      {
+        if (hc_atomic_inc (&hashes_shown[DIGESTS_OFFSET]) == 0)
+        {
+          mark_hash (plains_buf, d_return_buf, SALT_POS, digests_cnt, 0, DIGESTS_OFFSET + 0, gid, 0, 0, 0);
+        }
+
+        return;
+      }
+    }
+  }
 
   /*
    * Verify if decompressed data is either:
diff --git a/docs/changes.txt b/docs/changes.txt
index 93a8f237e..54866cf60 100644
--- a/docs/changes.txt
+++ b/docs/changes.txt
@@ -36,6 +36,7 @@
 - Backend devices: In non -S mode, limit the number of workitems so that no more than 4GB of host memory is required per backend device
 - Backend types: The default filter for the device types is now set so that only the GPU is used, except for APPLE, where we set CPU
 - Benchmark: Update benchmark_deep.pl with new hash modes added (also new hash modes which were added with v6.2.3)
+- Electrum Wallet: Added new entropy-based check to test whether the decryption was successful or not
 - Module Optimizers: Added OPTS_TYPE_MAXIMUM_THREADS to deactivate the else branch route in the section to find -T before compilation
 - Makefile: Added wildcard include src/modules/module_*.mk directive so that plugin developers can add 3rd party libraries for their plugins
 - Rejects: Disabled checking of the minimum and maximum length of the password candidate in attack-mode 9 because they are incompatible