diff --git a/fips202/fips202.h b/fips202/fips202.h
index 87454abc9..c80e57ac5 100644
--- a/fips202/fips202.h
+++ b/fips202/fips202.h
@@ -35,20 +35,6 @@ typedef struct
     uint64_t ctx[25];
 } shake256ctx;
 
-/**
- * Bare Keccak implementation for absorbing input data into the Keccak state.
- *
- * This function performs the absorb step of the Keccak cryptographic hash function.
- *
- * @param s Pointer to the Keccak state array. This array must contain at least 25 elements of type uint64_t.
- * @param r Rate in bytes. Specifies the rate parameter of the Keccak function, which determines how much
- *        data is processed per permutation.
- * @param m Pointer to the input data to be absorbed into the state.
- * @param mlen Length of the input data in bytes.
- * @param p Domain separation byte.
- */
-void keccak_absorb(uint64_t *s, uint32_t r, const uint8_t *m, size_t mlen, uint8_t p);
-
 /**
  * Squeezes blocks of data from the Keccak state.
  *
diff --git a/fips202/fips202x.c b/fips202/fips202x.c
index 8aa1145f3..545984052 100644
--- a/fips202/fips202x.c
+++ b/fips202/fips202x.c
@@ -2,6 +2,7 @@
 #include <string.h>
 #include "fips202x.h"
 #include "fips202.h"
+#include "keccakf1600.h"
 
 #define KECCAK_CTX 25
 
@@ -13,10 +14,49 @@ static void keccak_absorb_x4(uint64_t *s, uint32_t r,
                              size_t inlen,
                              uint8_t p) {
 
-    keccak_absorb(s + KECCAK_CTX * 0, r, in0, inlen, p);
-    keccak_absorb(s + KECCAK_CTX * 1, r, in1, inlen, p);
-    keccak_absorb(s + KECCAK_CTX * 2, r, in2, inlen, p);
-    keccak_absorb(s + KECCAK_CTX * 3, r, in3, inlen, p);
+    while (inlen >= r) {
+
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 0, in0, 0, r);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 1, in1, 0, r);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 2, in2, 0, r);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 3, in3, 0, r);
+
+        KeccakF1600_StatePermute(s + KECCAK_CTX * 0);
+        KeccakF1600_StatePermute(s + KECCAK_CTX * 1);
+        KeccakF1600_StatePermute(s + KECCAK_CTX * 2);
+        KeccakF1600_StatePermute(s + KECCAK_CTX * 3);
+
+        in0 += r;
+        in1 += r;
+        in2 += r;
+        in3 += r;
+        inlen -= r;
+    }
+
+    if (inlen > 0) {
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 0, in0, 0, inlen);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 1, in1, 0, inlen);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 2, in2, 0, inlen);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 3, in3, 0, inlen);
+    }
+
+    if (inlen == r - 1) {
+        p |= 128;
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 0, &p, inlen, 1);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 1, &p, inlen, 1);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 2, &p, inlen, 1);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 3, &p, inlen, 1);
+    } else {
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 0, &p, inlen, 1);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 1, &p, inlen, 1);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 2, &p, inlen, 1);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 3, &p, inlen, 1);
+        p = 128;
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 0, &p, r - 1, 1);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 1, &p, r - 1, 1);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 2, &p, r - 1, 1);
+        KeccakF1600_StateXORBytes(s + KECCAK_CTX * 3, &p, r - 1, 1);
+    }
 }
 
 static void keccak_squeezeblocks_x4(uint8_t *out0,
@@ -27,10 +67,23 @@ static void keccak_squeezeblocks_x4(uint8_t *out0,
                                     uint64_t *s,
                                     uint32_t r) {
 
-    keccak_squeezeblocks(out0, nblocks, s + KECCAK_CTX * 0, r);
-    keccak_squeezeblocks(out1, nblocks, s + KECCAK_CTX * 1, r);
-    keccak_squeezeblocks(out2, nblocks, s + KECCAK_CTX * 2, r);
-    keccak_squeezeblocks(out3, nblocks, s + KECCAK_CTX * 3, r);
+    while (nblocks > 0) {
+        KeccakF1600_StatePermute(s + KECCAK_CTX * 0);
+        KeccakF1600_StatePermute(s + KECCAK_CTX * 1);
+        KeccakF1600_StatePermute(s + KECCAK_CTX * 2);
+        KeccakF1600_StatePermute(s + KECCAK_CTX * 3);
+
+        KeccakF1600_StateExtractBytes(s + KECCAK_CTX * 0, out0, 0, r);
+        KeccakF1600_StateExtractBytes(s + KECCAK_CTX * 1, out1, 0, r);
+        KeccakF1600_StateExtractBytes(s + KECCAK_CTX * 2, out2, 0, r);
+        KeccakF1600_StateExtractBytes(s + KECCAK_CTX * 3, out3, 0, r);
+
+        out0 += r;
+        out1 += r;
+        out2 += r;
+        out3 += r;
+        nblocks--;
+    }
 }
 
 uint64_t *keccakx_get_lane_state(keccakx4_state *state, size_t index) {