fix(sha256): Add extra checks against message size when constructing …

…msg blocks (#5861)

# Description

## Problem\*

Resolves <!-- Link to GitHub Issue -->

Issue found in zk passport
https://github.com/ocelots-app/passport-verifier/blob/47e9464e7e782b07b6d791bf1d13257fce2f486b/crates/lib/data-check/integrity/src/lib.nr#L118
when performing sha on a message with a large padding.

## Summary\*

The current sha algorithm accounts for message padding, but only where
ithe padding is still contained in the block we are compressing. For the
case where we have a padding that extends multiple blocks past the
message size we end up with a correctness error. We need to add more
checks against the message size to make sure we are comrpessing the
correct msg block.

An increase in gate count is expected from these changes. 

## Additional Context



## Documentation\*

Check one:
- [X] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [X] I have tested the changes locally.
- [X] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

---------

Co-authored-by: Michael J Klein <michaeljklein@users.noreply.github.com>

noir_stdlib/src/hash/sha256.nr

@@ -67,18 +67,11 @@ fn verify_msg_block<let N: u32>(
 
     for k in msg_start..msg_end {
         if k as u64 < message_size {
+            assert_eq(msg_block[msg_byte_ptr], msg[k]);
             msg_byte_ptr = msg_byte_ptr + 1;
         }
     }
 
-    for i in 0..BLOCK_SIZE {
-        if i as u64 >= msg_byte_ptr {
-            assert_eq(msg_block[i], 0);
-        } else {
-            assert_eq(msg_block[i], msg[msg_start + i - extra_bytes]);
-        }
-    }
-
     msg_byte_ptr
 }
 
@@ -93,35 +86,51 @@ pub fn sha256_var<let N: u32>(msg: [u8; N], message_size: u64) -> [u8; 32] {
     let mut msg_byte_ptr = 0; // Pointer into msg_block
 
     for i in 0..num_blocks {
+        let msg_start = BLOCK_SIZE * i;
         let (new_msg_block, new_msg_byte_ptr) = unsafe {
-            build_msg_block_iter(msg, message_size, BLOCK_SIZE * i)
+            build_msg_block_iter(msg, message_size, msg_start)
         };
-        msg_block = new_msg_block;
+        if msg_start as u64 < message_size {
+            msg_block = new_msg_block;
+        }
 
         if !is_unconstrained() {
             // Verify the block we are compressing was appropriately constructed
-            msg_byte_ptr = verify_msg_block(msg, message_size, msg_block, BLOCK_SIZE * i);
-        } else {
+            let new_msg_byte_ptr = verify_msg_block(msg, message_size, msg_block, msg_start);
+            if msg_start as u64 < message_size {
+                msg_byte_ptr = new_msg_byte_ptr;
+            }
+        } else if msg_start as u64 < message_size {
             msg_byte_ptr = new_msg_byte_ptr;
         }
 
-        // Compress the block
-        h = sha256_compression(msg_u8_to_u32(msg_block), h);
+        // If the block is filled, compress it. 
+        // An un-filled block is handled after this loop.
+        if msg_byte_ptr == 64 {
+            h = sha256_compression(msg_u8_to_u32(msg_block), h);
+        }
     }
 
     let modulo = N % BLOCK_SIZE;
     // Handle setup of the final msg block.
     // This case is only hit if the msg is less than the block size, 
     // or our message cannot be evenly split into blocks. 
     if modulo != 0 {
+        let msg_start = BLOCK_SIZE * num_blocks;
         let (new_msg_block, new_msg_byte_ptr) = unsafe {
-            build_msg_block_iter(msg, message_size, BLOCK_SIZE * num_blocks)
+            build_msg_block_iter(msg, message_size, msg_start)
         };
-        msg_block = new_msg_block;
+
+        if msg_start as u64 < message_size {
+            msg_block = new_msg_block;
+        }
 
         if !is_unconstrained() {
-            msg_byte_ptr = verify_msg_block(msg, message_size, msg_block, BLOCK_SIZE * num_blocks);
-        } else {
+            let new_msg_byte_ptr = verify_msg_block(msg, message_size, msg_block, msg_start);
+            if msg_start as u64 < message_size {
+                msg_byte_ptr = new_msg_byte_ptr;
+            }
+        } else if msg_start as u64 < message_size {
             msg_byte_ptr = new_msg_byte_ptr;
         }
     }

test_programs/execution_success/sha256_regression/Prover.toml

@@ -2,8 +2,13 @@ msg_just_over_block = [102, 114, 111, 109, 58, 114, 117, 110, 110, 105, 101, 114
 msg_multiple_of_block = [102, 114, 111, 109, 58, 114, 117, 110, 110, 105, 101, 114, 46, 108, 101, 97, 103, 117, 101, 115, 46, 48, 106, 64, 105, 99, 108, 111, 117, 100, 46, 99, 111, 109, 13, 10, 99, 111, 110, 116, 101, 110, 116, 45, 116, 121, 112, 101, 58, 116, 101, 120, 116, 47, 112, 108, 97, 105, 110, 59, 32, 99, 104, 97, 114, 115, 101, 116, 61, 117, 115, 45, 97, 115, 99, 105, 105, 13, 10, 109, 105, 109, 101, 45, 118, 101, 114, 115, 105, 111, 110, 58, 49, 46, 48, 32, 40, 77, 97, 99, 32, 79, 83, 32, 88, 32, 77, 97, 105, 108, 32, 49, 54, 46, 48, 32, 92, 40, 51, 55, 51, 49, 46, 53, 48, 48, 46, 50, 51, 49, 92, 41, 41, 13, 10, 115, 117, 98, 106, 101, 99, 116, 58, 72, 101, 108, 108, 111, 13, 10, 109, 101, 115, 115, 97, 103, 101, 45, 105, 100, 58, 60, 56, 70, 56, 49, 57, 68, 51, 50, 45, 66, 54, 65, 67, 45, 52, 56, 57, 68, 45, 57, 55, 55, 70, 45, 52, 51, 56, 66, 66, 67, 52, 67, 65, 66, 50, 55, 64, 109, 101, 46, 99, 111, 109, 62, 13, 10, 100, 97, 116, 101, 58, 83, 97, 116, 44, 32, 50, 54, 32, 65, 117, 103, 32, 50, 48, 50, 51, 32, 49, 50, 58, 50, 53, 58, 50, 50, 32, 43, 48, 52, 48, 48, 13, 10, 116, 111, 58, 122, 107, 101, 119, 116, 101, 115, 116, 64, 103, 109, 97, 105, 108, 46, 99, 111, 109, 13, 10, 100, 107, 105, 109, 45, 115, 105, 103, 110, 97, 116, 117, 114, 101, 58, 118, 61, 49, 59, 32, 97, 61, 114, 115, 97, 45, 115, 104, 97, 50, 53, 54, 59, 32, 99, 61, 114, 101, 108, 97, 120, 101, 100, 47, 114, 101, 108, 97, 120, 101, 100, 59, 32, 100, 61, 105, 99, 108, 111, 117, 100, 46, 99, 111, 109, 59, 32, 115, 61, 49, 97, 49, 104, 97, 105, 59, 32, 116, 61, 49, 54, 57, 51, 48, 51, 56, 51, 51, 55, 59, 32, 98, 104, 61, 55, 120, 81, 77, 68, 117, 111, 86, 86, 85, 52, 109, 48, 87, 48, 87, 82, 86, 83, 114, 86, 88, 77, 101, 71, 83, 73, 65, 83, 115, 110, 117, 99, 75, 57, 100, 74, 115, 114, 99, 43, 118, 85, 61, 59, 32, 104, 61, 102, 114, 111, 109, 58, 67, 111, 110, 116, 101, 110, 116, 45, 84, 121, 112, 101, 58, 77, 105, 109, 101, 45, 86, 101, 114, 115, 105, 111, 110, 58, 83, 117, 98, 106, 101, 99]
 msg_just_under_block = [102, 114, 111, 109, 58, 114, 117, 110, 110, 105, 101, 114, 46, 108, 101, 97, 103, 117, 101, 115, 46, 48, 106, 64, 105, 99, 108, 111, 117, 100, 46, 99, 111, 109, 13, 10, 99, 111, 110, 116, 101, 110, 116, 45, 116, 121, 112, 101, 58, 116, 101, 120, 116, 47, 112, 108, 97, 105, 110, 59]
 msg_big_not_block_multiple = [102, 114, 111, 109, 58, 114, 117, 110, 110, 105, 101, 114, 46, 108, 101, 97, 103, 117, 101, 115, 46, 48, 106, 64, 105, 99, 108, 111, 117, 100, 46, 99, 111, 109, 13, 10, 99, 111, 110, 116, 101, 110, 116, 45, 116, 121, 112, 101, 58, 116, 101, 120, 116, 47, 112, 108, 97, 105, 110, 59, 32, 99, 104, 97, 114, 115, 101, 116, 61, 117, 115, 45, 97, 115, 99, 105, 105, 13, 10, 109, 105, 109, 101, 45, 118, 101, 114, 115, 105, 111, 110, 58, 49, 46, 48, 32, 40, 77, 97, 99, 32, 79, 83, 32, 88, 32, 77, 97, 105, 108, 32, 49, 54, 46, 48, 32, 92, 40, 51, 55, 51, 49, 46, 53, 48, 48, 46, 50, 51, 49, 92, 41, 41, 13, 10, 115, 117, 98, 106, 101, 99, 116, 58, 72, 101, 108, 108, 111, 13, 10, 109, 101, 115, 115, 97, 103, 101, 45, 105, 100, 58, 60, 56, 70, 56, 49, 57, 68, 51, 50, 45, 66, 54, 65, 67, 45, 52, 56, 57, 68, 45, 57, 55, 55, 70, 45, 52, 51, 56, 66, 66, 67, 52, 67, 65, 66, 50, 55, 64, 109, 101, 46, 99, 111, 109, 62, 13, 10, 100, 97, 116, 101, 58, 83, 97, 116, 44, 32, 50, 54, 32, 65, 117, 103, 32, 50, 48, 50, 51, 32, 49, 50, 58, 50, 53, 58, 50, 50, 32, 43, 48, 52, 48, 48, 13, 10, 116, 111, 58, 122, 107, 101, 119, 116, 101, 115, 116, 64, 103, 109, 97, 105, 108, 46, 99, 111, 109, 13, 10, 100, 107, 105, 109, 45, 115, 105, 103, 110, 97, 116, 117, 114, 101, 58, 118, 61, 49, 59, 32, 97, 61, 114, 115, 97, 45, 115, 104, 97, 50, 53, 54, 59, 32, 99, 61, 114, 101, 108, 97, 120, 101, 100, 47, 114, 101, 108, 97, 120, 101, 100, 59, 32, 100, 61, 105, 99, 108, 111, 117, 100, 46, 99, 111, 109, 59, 32, 115, 61, 49, 97, 49, 104, 97, 105, 59, 32, 116, 61, 49, 54, 57, 51, 48, 51, 56, 51, 51, 55, 59, 32, 98, 104, 61, 55, 120, 81, 77, 68, 117, 111, 86, 86, 85, 52, 109, 48, 87, 48, 87, 82, 86, 83, 114, 86, 88, 77, 101, 71, 83, 73, 65, 83, 115, 110, 117, 99, 75, 57, 100, 74, 115, 114, 99, 43, 118, 85, 61, 59, 32, 104, 61, 102, 114, 111, 109, 58, 67, 111, 110, 116, 101, 110, 116, 45, 84, 121, 112, 101, 58, 77, 105, 109, 101, 45, 86, 101, 114, 115, 105, 111, 110, 58, 83, 117, 98, 106, 101, 99, 116, 58, 77, 101, 115, 115, 97, 103, 101, 45, 73, 100, 58, 68, 97, 116, 101, 58, 116, 111, 59, 32, 98, 61]
+msg_big_with_padding = [48, 130, 1, 37, 2, 1, 0, 48, 11, 6, 9, 96, 134, 72, 1, 101, 3, 4, 2, 1, 48, 130, 1, 17, 48, 37, 2, 1, 1, 4, 32, 176, 223, 31, 133, 108, 84, 158, 102, 70, 11, 165, 175, 196, 12, 201, 130, 25, 131, 46, 125, 156, 194, 28, 23, 55, 133, 157, 164, 135, 136, 220, 78, 48, 37, 2, 1, 2, 4, 32, 190, 82, 180, 235, 222, 33, 79, 50, 152, 136, 142, 35, 116, 224, 6, 242, 156, 141, 128, 248, 10, 61, 98, 86, 248, 45, 207, 210, 90, 232, 175, 38, 48, 37, 2, 1, 3, 4, 32, 0, 194, 104, 108, 237, 246, 97, 230, 116, 198, 69, 110, 26, 87, 17, 89, 110, 199, 108, 250, 36, 21, 39, 87, 110, 102, 250, 213, 174, 131, 171, 174, 48, 37, 2, 1, 11, 4, 32, 136, 155, 87, 144, 111, 15, 152, 127, 85, 25, 154, 81, 20, 58, 51, 75, 193, 116, 234, 0, 60, 30, 29, 30, 183, 141, 72, 247, 255, 203, 100, 124, 48, 37, 2, 1, 12, 4, 32, 41, 234, 106, 78, 31, 11, 114, 137, 237, 17, 92, 71, 134, 47, 62, 78, 189, 233, 201, 214, 53, 4, 47, 189, 201, 133, 6, 121, 34, 131, 64, 142, 48, 37, 2, 1, 13, 4, 32, 91, 222, 210, 193, 62, 222, 104, 82, 36, 41, 138, 253, 70, 15, 148, 208, 156, 45, 105, 171, 241, 195, 185, 43, 217, 162, 146, 201, 222, 89, 238, 38, 48, 37, 2, 1, 14, 4, 32, 76, 123, 216, 13, 51, 227, 72, 245, 59, 193, 238, 166, 103, 49, 23, 164, 171, 188, 194, 197, 156, 187, 249, 28, 198, 95, 69, 15, 182, 56, 54, 38, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
+msg_big_no_padding = [48, 130, 1, 37, 2, 1, 0, 48, 11, 6, 9, 96, 134, 72, 1, 101, 3, 4, 2, 1, 48, 130, 1, 17, 48, 37, 2, 1, 1, 4, 32, 176, 223, 31, 133, 108, 84, 158, 102, 70, 11, 165, 175, 196, 12, 201, 130, 25, 131, 46, 125, 156, 194, 28, 23, 55, 133, 157, 164, 135, 136, 220, 78, 48, 37, 2, 1, 2, 4, 32, 190, 82, 180, 235, 222, 33, 79, 50, 152, 136, 142, 35, 116, 224, 6, 242, 156, 141, 128, 248, 10, 61, 98, 86, 248, 45, 207, 210, 90, 232, 175, 38, 48, 37, 2, 1, 3, 4, 32, 0, 194, 104, 108, 237, 246, 97, 230, 116, 198, 69, 110, 26, 87, 17, 89, 110, 199, 108, 250, 36, 21, 39, 87, 110, 102, 250, 213, 174, 131, 171, 174, 48, 37, 2, 1, 11, 4, 32, 136, 155, 87, 144, 111, 15, 152, 127, 85, 25, 154, 81, 20, 58, 51, 75, 193, 116, 234, 0, 60, 30, 29, 30, 183, 141, 72, 247, 255, 203, 100, 124, 48, 37, 2, 1, 12, 4, 32, 41, 234, 106, 78, 31, 11, 114, 137, 237, 17, 92, 71, 134, 47, 62, 78, 189, 233, 201, 214, 53, 4, 47, 189, 201, 133, 6, 121, 34, 131, 64, 142, 48, 37, 2, 1, 13, 4, 32, 91, 222, 210, 193, 62, 222, 104, 82, 36, 41, 138, 253, 70, 15, 148, 208, 156, 45, 105, 171, 241, 195, 185, 43, 217, 162, 146, 201, 222, 89, 238, 38, 48, 37, 2, 1, 14, 4, 32, 76, 123, 216, 13, 51, 227, 72, 245, 59, 193, 238, 166, 103, 49, 23, 164, 171, 188, 194, 197, 156, 187, 249, 28, 198, 95, 69, 15, 182, 56, 54, 38]
+message_size = 297
+
 #  Results matched against ethers library
 result_just_over_block = [91, 122, 146, 93, 52, 109, 133, 148, 171, 61, 156, 70, 189, 238, 153, 7, 222, 184, 94, 24, 65, 114, 192, 244, 207, 199, 87, 232, 192, 224, 171, 207]
 result_multiple_of_block = [116, 90, 151, 31, 78, 22, 138, 180, 211, 189, 69, 76, 227, 200, 155, 29, 59, 123, 154, 60, 47, 153, 203, 129, 157, 251, 48, 2, 79, 11, 65, 47]
 result_just_under_block = [143, 140, 76, 173, 222, 123, 102, 68, 70, 149, 207, 43, 39, 61, 34, 79, 216, 252, 213, 165, 74, 16, 110, 74, 29, 64, 138, 167, 30, 1, 9, 119]
 result_big = [112, 144, 73, 182, 208, 98, 9, 238, 54, 229, 61, 145, 222, 17, 72, 62, 148, 222, 186, 55, 192, 82, 220, 35, 66, 47, 193, 200, 22, 38, 26, 186]
+result_big_with_padding = [32, 85, 108, 174, 127, 112, 178, 182, 8, 43, 134, 123, 192, 211, 131, 66, 184, 240, 212, 181, 240, 180, 106, 195, 24, 117, 54, 129, 19, 10, 250, 53]

test_programs/execution_success/sha256_regression/src/main.nr

@@ -1,3 +1,4 @@
+// A bunch of different test cases for sha256_var in the stdlib
 fn main(
     msg_just_over_block: [u8; 68],
     result_just_over_block: pub [u8; 32],
@@ -7,7 +8,13 @@ fn main(
     msg_just_under_block: [u8; 60],
     result_just_under_block: pub [u8; 32],
     msg_big_not_block_multiple: [u8; 472],
-    result_big: pub [u8; 32]
+    result_big: pub [u8; 32],
+    // This message is only 297 elements and we want to hash only a variable amount
+    msg_big_with_padding: [u8; 700],
+    // This is the same as `msg_big_with_padding` but with no padding
+    msg_big_no_padding: [u8; 297],
+    message_size: u64,
+    result_big_with_padding: pub [u8; 32]
 ) {
     let hash = std::hash::sha256_var(msg_just_over_block, msg_just_over_block.len() as u64);
     assert_eq(hash, result_just_over_block);
@@ -23,4 +30,10 @@ fn main(
         msg_big_not_block_multiple.len() as u64
     );
     assert_eq(hash, result_big);
+
+    let hash_padding = std::hash::sha256_var(msg_big_with_padding, message_size);
+    assert_eq(hash_padding, result_big_with_padding);
+
+    let hash_no_padding = std::hash::sha256_var(msg_big_no_padding, message_size);
+    assert_eq(hash_no_padding, result_big_with_padding);
 }