diff --git a/server/src/chat/transport/slack/verify.rs b/server/src/chat/transport/slack/verify.rs
index 9855c4dc..0a8c60dd 100644
--- a/server/src/chat/transport/slack/verify.rs
+++ b/server/src/chat/transport/slack/verify.rs
@@ -2,6 +2,12 @@
 
 use std::fmt::Write as FmtWrite;
 
+use hmac::{Hmac, KeyInit, Mac};
+use sha2::Sha256;
+use subtle::ConstantTimeEq;
+
+type HmacSha256 = Hmac<Sha256>;
+
 /// Verify the Slack request signature using HMAC-SHA256.
 ///
 /// Slack sends `X-Slack-Signature` and `X-Slack-Request-Timestamp` headers.
@@ -15,163 +21,22 @@ pub(super) fn verify_slack_signature(
     body: &[u8],
     signature: &str,
 ) -> bool {
-    // Compute HMAC-SHA256 manually using the signing secret.
-    // Slack signature format: v0={hex(HMAC-SHA256(secret, "v0:{ts}:{body}"))}
-    let base_string = format!("v0:{timestamp}:");
-
-    // Simple HMAC-SHA256 implementation using ring-style approach.
-    // We use the hmac crate pattern with SHA-256.
-    // Since we don't want to add a dependency, we'll use a manual approach:
-    // HMAC(K, m) = H((K' ^ opad) || H((K' ^ ipad) || m))
-    // where K' is the key padded/hashed to block size.
-
-    let key = signing_secret.as_bytes();
-    let block_size = 64; // SHA-256 block size
-
-    // If key is longer than block size, hash it first.
-    let key_block = if key.len() > block_size {
-        let digest = sha256(key);
-        let mut k = vec![0u8; block_size];
-        k[..32].copy_from_slice(&digest);
-        k
-    } else {
-        let mut k = vec![0u8; block_size];
-        k[..key.len()].copy_from_slice(key);
-        k
-    };
-
-    // Inner and outer padded keys.
-    let mut ipad = vec![0x36u8; block_size];
-    let mut opad = vec![0x5cu8; block_size];
-    for i in 0..block_size {
-        ipad[i] ^= key_block[i];
-        opad[i] ^= key_block[i];
-    }
-
-    // Inner hash: H(ipad || message)
-    let mut inner_data = ipad;
-    inner_data.extend_from_slice(base_string.as_bytes());
-    inner_data.extend_from_slice(body);
-    let inner_hash = sha256(&inner_data);
-
-    // Outer hash: H(opad || inner_hash)
-    let mut outer_data = opad;
-    outer_data.extend_from_slice(&inner_hash);
-    let hmac_result = sha256(&outer_data);
+    let mut mac = HmacSha256::new_from_slice(signing_secret.as_bytes())
+        .expect("HMAC can take key of any size");
+    mac.update(b"v0:");
+    mac.update(timestamp.as_bytes());
+    mac.update(b":");
+    mac.update(body);
+    let result = mac.finalize().into_bytes();
 
     // Format as "v0={hex}"
     let mut expected = String::from("v0=");
-    for byte in &hmac_result {
+    for byte in &result {
         write!(expected, "{byte:02x}").unwrap();
     }
 
-    // Constant-time comparison.
-    constant_time_eq(expected.as_bytes(), signature.as_bytes())
-}
-
-/// Minimal SHA-256 implementation (no external dependency).
-///
-/// This follows FIPS 180-4.  Only used for HMAC signature verification,
-/// not for any security-critical path beyond webhook authentication.
-fn sha256(data: &[u8]) -> [u8; 32] {
-    let mut h: [u32; 8] = [
-        0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab,
-        0x5be0cd19,
-    ];
-
-    let k: [u32; 64] = [
-        0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4,
-        0xab1c5ed5, 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe,
-        0x9bdc06a7, 0xc19bf174, 0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f,
-        0x4a7484aa, 0x5cb0a9dc, 0x76f988da, 0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
-        0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc,
-        0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85, 0xa2bfe8a1, 0xa81a664b,
-        0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070, 0x19a4c116,
-        0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
-        0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7,
-        0xc67178f2,
-    ];
-
-    // Pre-processing: padding
-    let bit_len = (data.len() as u64) * 8;
-    let mut padded = data.to_vec();
-    padded.push(0x80);
-    while (padded.len() % 64) != 56 {
-        padded.push(0);
-    }
-    padded.extend_from_slice(&bit_len.to_be_bytes());
-
-    // Process each 512-bit block
-    for chunk in padded.chunks_exact(64) {
-        let mut w = [0u32; 64];
-        for i in 0..16 {
-            w[i] = u32::from_be_bytes([
-                chunk[4 * i],
-                chunk[4 * i + 1],
-                chunk[4 * i + 2],
-                chunk[4 * i + 3],
-            ]);
-        }
-        for i in 16..64 {
-            let s0 = w[i - 15].rotate_right(7) ^ w[i - 15].rotate_right(18) ^ (w[i - 15] >> 3);
-            let s1 = w[i - 2].rotate_right(17) ^ w[i - 2].rotate_right(19) ^ (w[i - 2] >> 10);
-            w[i] = w[i - 16]
-                .wrapping_add(s0)
-                .wrapping_add(w[i - 7])
-                .wrapping_add(s1);
-        }
-
-        let [mut a, mut b, mut c, mut d, mut e, mut f, mut g, mut hh] = h;
-
-        for i in 0..64 {
-            let s1 = e.rotate_right(6) ^ e.rotate_right(11) ^ e.rotate_right(25);
-            let ch = (e & f) ^ ((!e) & g);
-            let temp1 = hh
-                .wrapping_add(s1)
-                .wrapping_add(ch)
-                .wrapping_add(k[i])
-                .wrapping_add(w[i]);
-            let s0 = a.rotate_right(2) ^ a.rotate_right(13) ^ a.rotate_right(22);
-            let maj = (a & b) ^ (a & c) ^ (b & c);
-            let temp2 = s0.wrapping_add(maj);
-
-            hh = g;
-            g = f;
-            f = e;
-            e = d.wrapping_add(temp1);
-            d = c;
-            c = b;
-            b = a;
-            a = temp1.wrapping_add(temp2);
-        }
-
-        h[0] = h[0].wrapping_add(a);
-        h[1] = h[1].wrapping_add(b);
-        h[2] = h[2].wrapping_add(c);
-        h[3] = h[3].wrapping_add(d);
-        h[4] = h[4].wrapping_add(e);
-        h[5] = h[5].wrapping_add(f);
-        h[6] = h[6].wrapping_add(g);
-        h[7] = h[7].wrapping_add(hh);
-    }
-
-    let mut result = [0u8; 32];
-    for (i, val) in h.iter().enumerate() {
-        result[4 * i..4 * i + 4].copy_from_slice(&val.to_be_bytes());
-    }
-    result
-}
-
-/// Constant-time byte comparison.
-fn constant_time_eq(a: &[u8], b: &[u8]) -> bool {
-    if a.len() != b.len() {
-        return false;
-    }
-    let mut diff = 0u8;
-    for (x, y) in a.iter().zip(b.iter()) {
-        diff |= x ^ y;
-    }
-    diff == 0
+    // Constant-time comparison to prevent timing attacks.
+    expected.as_bytes().ct_eq(signature.as_bytes()).into()
 }
 
 // ── Tests ───────────────────────────────────────────────────────────────
@@ -189,7 +54,6 @@ mod tests {
         let timestamp = "1531420618";
         let body = b"token=xyzz0WbapA4vBCDEFasx0q6G&team_id=T1DC2JH3J&team_domain=testteamnow&channel_id=G8PSS9T3V&channel_name=foobar&user_id=U2CERLKJA&user_name=roadrunner&command=%2Fwebhook-collect&text=&response_url=https%3A%2F%2Fhooks.slack.com%2Fcommands%2FT1DC2JH3J%2F397700885554%2F96rGlfmibIGlgcZRskXaIFfN&trigger_id=398738663015.47445629121.803a0bc887a14d10d2c659f";
 
-        // Compute expected signature for this test case.
         let sig = compute_test_signature(secret, timestamp, body);
 
         assert!(verify_slack_signature(secret, timestamp, body, &sig));
@@ -223,83 +87,22 @@ mod tests {
         ));
     }
 
-    /// Helper to compute a test signature using our sha256 + HMAC implementation.
+    /// Helper to compute a test signature using `Hmac<Sha256>`.
     fn compute_test_signature(secret: &str, timestamp: &str, body: &[u8]) -> String {
         use std::fmt::Write;
 
-        let key = secret.as_bytes();
-        let block_size = 64;
-        let key_block = if key.len() > block_size {
-            let digest = sha256(key);
-            let mut k = vec![0u8; block_size];
-            k[..32].copy_from_slice(&digest);
-            k
-        } else {
-            let mut k = vec![0u8; block_size];
-            k[..key.len()].copy_from_slice(key);
-            k
-        };
+        let mut mac =
+            HmacSha256::new_from_slice(secret.as_bytes()).expect("HMAC can take key of any size");
+        mac.update(b"v0:");
+        mac.update(timestamp.as_bytes());
+        mac.update(b":");
+        mac.update(body);
+        let result = mac.finalize().into_bytes();
 
-        let mut ipad = vec![0x36u8; block_size];
-        let mut opad = vec![0x5cu8; block_size];
-        for i in 0..block_size {
-            ipad[i] ^= key_block[i];
-            opad[i] ^= key_block[i];
+        let mut sig = String::from("v0=");
+        for byte in &result {
+            write!(sig, "{byte:02x}").unwrap();
         }
-
-        let base_string = format!("v0:{timestamp}:");
-        let mut inner_data = ipad;
-        inner_data.extend_from_slice(base_string.as_bytes());
-        inner_data.extend_from_slice(body);
-        let inner_hash = sha256(&inner_data);
-
-        let mut outer_data = opad;
-        outer_data.extend_from_slice(&inner_hash);
-        let hmac_result = sha256(&outer_data);
-
-        let mut expected = String::from("v0=");
-        for byte in &hmac_result {
-            write!(expected, "{byte:02x}").unwrap();
-        }
-        expected
-    }
-
-    // ── SHA-256 implementation ──────────────────────────────────────────
-
-    #[test]
-    fn sha256_empty_string() {
-        let result = sha256(b"");
-        let hex: String = result.iter().map(|b| format!("{b:02x}")).collect();
-        assert_eq!(
-            hex,
-            "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
-        );
-    }
-
-    #[test]
-    fn sha256_hello_world() {
-        let result = sha256(b"hello world");
-        let hex: String = result.iter().map(|b| format!("{b:02x}")).collect();
-        assert_eq!(
-            hex,
-            "b94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9"
-        );
-    }
-
-    // ── Constant-time comparison ────────────────────────────────────────
-
-    #[test]
-    fn constant_time_eq_same_values() {
-        assert!(constant_time_eq(b"hello", b"hello"));
-    }
-
-    #[test]
-    fn constant_time_eq_different_values() {
-        assert!(!constant_time_eq(b"hello", b"world"));
-    }
-
-    #[test]
-    fn constant_time_eq_different_lengths() {
-        assert!(!constant_time_eq(b"hello", b"hi"));
+        sig
     }
 }