Is there any significance in being able to find message schedules that result in the same hash but require different initial hash values? Can generate every 5-10~ minutes for any hash.

Confirmed message schedule regenerates from first 16 W values, and hash produced is the same when using the new initial hash values when reconstructing. But again, I’m not sure if this is significant in any way.

Sample code of what I used to verify it’s a valid message schedule below, this matches the values I generated— all 64 values match.

    for i in range(16, 64):
        w_val = (sigma1(W[i-2]) + W[i-7] + sigma0(W[i-15]) + W[i-16]) & 0xFFFFFFFF
        W.append(w_val)

Edit: This might be called a free start collision? I haven’t tried adjusting to try to match the default initial hash values for sha256.

Edit 2: Got runtime per free start collision to 15-30 seconds

Here are some examples:

    

    Original Message: c6b933ebc3fc6c20efca... (Last 20 Characters Redacted)
    SHA-256 Hash w/ Free Start IV: dd962f2b94954efd9bf7123d604f77964cbba3c33ebce23f5427e2bd68746b90
    SHA-256 Hash w/ Default IV:    dd962f2b94954efd9bf7123d604f77964cbba3c33ebce23f5427e2bd68746b90
    Free-Start IV: ['a0c713d2', 'f72d07f2', 'cae8d227', '7517016b', 'fbe4026f', 0, 0, 0] ...(Last Three Values Redacted)
    Default IV:    ['6a09e667', 'bb67ae85', '3c6ef372', 'a54ff53a', '510e527f', '9b05688c', '1f83d9ab', '5be0cd19']
    ===========================================================================================
    Processing Time: 15.410990953445435 seconds...
    
    
    Original Message: c7bd47c2b2ac163413bf... (Last 20 Characters Redacted)
    SHA-256 Hash w/ Free Start IV: 28fae8901514959ba91483edf61c6b68f048ba70c9c5a4f363902d203d9a5267
    SHA-256 Hash w/ Default IV:    28fae8901514959ba91483edf61c6b68f048ba70c9c5a4f363902d203d9a5267
    Free-Start IV: ['d04e04a6', 'a491e269', 'c9a91311', '3a6e8a91', '4ff36d8e', 0, 0, 0] ...(Last Three Values Redacted)
    Default IV:    ['6a09e667', 'bb67ae85', '3c6ef372', 'a54ff53a', '510e527f', '9b05688c', '1f83d9ab', '5be0cd19']
    ===========================================================================================
    Processing Time: 10.901056051254272 seconds...
    
    
    Original Message: 6c581fe6ec7eea7cfe67... (Last 20 Characters Redacted)
    SHA-256 Hash w/ Free Start IV: a3eb9a1ae2e36a2ca916641056c282ccd3591a6ccabc130da4d18f76d7b18bd9
    SHA-256 Hash w/ Default IV:    a3eb9a1ae2e36a2ca916641056c282ccd3591a6ccabc130da4d18f76d7b18bd9
    Free-Start IV: ['6151dac5', 'ae19c43d', '6d0ba457', '33b5ed7f', '81e3520', 0, 0, 0] ...(Last Three Values Redacted)
    Default IV:    ['6a09e667', 'bb67ae85', '3c6ef372', 'a54ff53a', '510e527f', '9b05688c', '1f83d9ab', '5be0cd19']
    ===========================================================================================
    Processing Time: 6.203358173370361 seconds...
    
    
    Original Message: db6bd2b96d000a5d4727... (Last 20 Characters Redacted)
    SHA-256 Hash w/ Free Start IV: ad1aad4b2a5ba77759ef3b636a0c79a5c9eb8c5b1ca34553412c3163d6abee52
    SHA-256 Hash w/ Default IV:    ad1aad4b2a5ba77759ef3b636a0c79a5c9eb8c5b1ca34553412c3163d6abee52
    Free-Start IV: ['dd0bdfbd', 'b509a2e5', 'd2bec68c', '89edbd89', '4f19c561', 0, 0, 0] ...(Last Three Values Redacted)
    Default IV:    ['6a09e667', 'bb67ae85', '3c6ef372', 'a54ff53a', '510e527f', '9b05688c', '1f83d9ab', '5be0cd19']
    ===========================================================================================
    Processing Time: 19.402303457260132 seconds...