diff --git a/crypto/fipsmodule/digest/digests.c b/crypto/fipsmodule/digest/digests.c
index 648278c6d0..88b45d2e5f 100644
--- a/crypto/fipsmodule/digest/digests.c
+++ b/crypto/fipsmodule/digest/digests.c
@@ -326,7 +326,7 @@ DEFINE_METHOD_FUNCTION(EVP_MD, EVP_sha512_256) {
 
 
 static void sha3_224_init(EVP_MD_CTX *ctx) {
-  CHECK(SHA3_Init(ctx->md_data, SHA3_PAD_CHAR, SHA3_224_DIGEST_BITLENGTH));
+  CHECK(SHA3_Init(ctx->md_data, SHA3_224_DIGEST_BITLENGTH));
 }
 
 static void sha3_224_update(EVP_MD_CTX *ctx, const void *data, size_t count) {
@@ -351,7 +351,7 @@ DEFINE_METHOD_FUNCTION(EVP_MD, EVP_sha3_224) {
 
 
 static void sha3_256_init(EVP_MD_CTX *ctx) {
-  CHECK(SHA3_Init(ctx->md_data, SHA3_PAD_CHAR, SHA3_256_DIGEST_BITLENGTH));
+  CHECK(SHA3_Init(ctx->md_data, SHA3_256_DIGEST_BITLENGTH));
 }
 
 static void sha3_256_update(EVP_MD_CTX *ctx, const void *data, size_t count) {
@@ -376,7 +376,7 @@ DEFINE_METHOD_FUNCTION(EVP_MD, EVP_sha3_256) {
 
 
 static void sha3_384_init(EVP_MD_CTX *ctx) {
-  CHECK(SHA3_Init(ctx->md_data, SHA3_PAD_CHAR, SHA3_384_DIGEST_BITLENGTH));
+  CHECK(SHA3_Init(ctx->md_data, SHA3_384_DIGEST_BITLENGTH));
 }
 
 static void sha3_384_update(EVP_MD_CTX *ctx, const void *data, size_t count) {
@@ -401,7 +401,7 @@ DEFINE_METHOD_FUNCTION(EVP_MD, EVP_sha3_384) {
 
 
 static void sha3_512_init(EVP_MD_CTX *ctx) {
-  CHECK(SHA3_Init(ctx->md_data, SHA3_PAD_CHAR, SHA3_512_DIGEST_BITLENGTH));
+  CHECK(SHA3_Init(ctx->md_data, SHA3_512_DIGEST_BITLENGTH));
 }
 
 static void sha3_512_update(EVP_MD_CTX *ctx, const void *data, size_t count) {
diff --git a/crypto/fipsmodule/sha/internal.h b/crypto/fipsmodule/sha/internal.h
index 2a42d6aa8a..3a0a1c37ce 100644
--- a/crypto/fipsmodule/sha/internal.h
+++ b/crypto/fipsmodule/sha/internal.h
@@ -408,7 +408,7 @@ int SHAKE_Final(uint8_t *md, KECCAK1600_CTX *ctx, size_t len);
 void SHA3_Reset(KECCAK1600_CTX *ctx);
 
 // SHA3_Init initialises |ctx| fields and returns 1 on success and 0 on failure.
-OPENSSL_EXPORT int SHA3_Init(KECCAK1600_CTX *ctx, uint8_t pad, size_t bitlen);
+OPENSSL_EXPORT int SHA3_Init(KECCAK1600_CTX *ctx, size_t bitlen);
 
 // SHA3_Update processes all data blocks that don't need pad through
 // |Keccak1600_Absorb| and returns 1 and 0 on failure.
diff --git a/crypto/fipsmodule/sha/sha3.c b/crypto/fipsmodule/sha/sha3.c
index c08f99e744..02c33cb238 100644
--- a/crypto/fipsmodule/sha/sha3.c
+++ b/crypto/fipsmodule/sha/sha3.c
@@ -14,7 +14,7 @@ uint8_t *SHA3_224(const uint8_t *data, size_t len,
                   uint8_t out[SHA3_224_DIGEST_LENGTH]) {
   FIPS_service_indicator_lock_state();
   KECCAK1600_CTX ctx;
-  int ok = (SHA3_Init(&ctx, SHA3_PAD_CHAR, SHA3_224_DIGEST_BITLENGTH) &&
+  int ok = (SHA3_Init(&ctx, SHA3_224_DIGEST_BITLENGTH) &&
             SHA3_Update(&ctx, data, len) &&
             SHA3_Final(out, &ctx));
 
@@ -31,7 +31,7 @@ uint8_t *SHA3_256(const uint8_t *data, size_t len,
                   uint8_t out[SHA3_256_DIGEST_LENGTH]) {
   FIPS_service_indicator_lock_state();
   KECCAK1600_CTX ctx;
-  int ok = (SHA3_Init(&ctx, SHA3_PAD_CHAR, SHA3_256_DIGEST_BITLENGTH) &&
+  int ok = (SHA3_Init(&ctx, SHA3_256_DIGEST_BITLENGTH) &&
             SHA3_Update(&ctx, data, len) &&
             SHA3_Final(out, &ctx));
 
@@ -48,7 +48,7 @@ uint8_t *SHA3_384(const uint8_t *data, size_t len,
                   uint8_t out[SHA3_384_DIGEST_LENGTH]) {
   FIPS_service_indicator_lock_state();
   KECCAK1600_CTX ctx;
-  int ok = (SHA3_Init(&ctx, SHA3_PAD_CHAR, SHA3_384_DIGEST_BITLENGTH) &&
+  int ok = (SHA3_Init(&ctx, SHA3_384_DIGEST_BITLENGTH) &&
             SHA3_Update(&ctx, data, len) &&
             SHA3_Final(out, &ctx));
 
@@ -65,7 +65,7 @@ uint8_t *SHA3_512(const uint8_t *data, size_t len,
                   uint8_t out[SHA3_512_DIGEST_LENGTH]) {
   FIPS_service_indicator_lock_state();
   KECCAK1600_CTX ctx;
-  int ok = (SHA3_Init(&ctx, SHA3_PAD_CHAR, SHA3_512_DIGEST_BITLENGTH) &&
+  int ok = (SHA3_Init(&ctx, SHA3_512_DIGEST_BITLENGTH) &&
             SHA3_Update(&ctx, data, len) &&
             SHA3_Final(out, &ctx));
 
@@ -109,49 +109,43 @@ uint8_t *SHAKE256(const uint8_t *data, const size_t in_len, uint8_t *out, size_t
   return out;
 }
 
-int SHAKE_Init(KECCAK1600_CTX *ctx, size_t block_size) {
-  // The SHAKE block size depends on the security level of the algorithm only
-  // It is independent of the output size
-  ctx->block_size = block_size;
-  return SHA3_Init(ctx, SHAKE_PAD_CHAR, 0);
+// FIPS202 APIs manage internal input/output buffer on top of Keccak1600 API layer
+static void FIPS202_Reset(KECCAK1600_CTX *ctx) {
+  memset(ctx->A, 0, sizeof(ctx->A));
+  ctx->buf_load = 0;
+  ctx->padded=0;
 }
 
-
-int SHAKE_Final(uint8_t *md, KECCAK1600_CTX *ctx, size_t len) {
-  ctx->md_size = len;
-  return SHA3_Final(md, ctx);
+static int FIPS202_Init(KECCAK1600_CTX *ctx, uint8_t pad, size_t block_size, size_t bit_len) {
+  if (pad != SHA3_PAD_CHAR && 
+      pad != SHAKE_PAD_CHAR) { 
+    return 0;
+  }
+      
+  if (block_size <= sizeof(ctx->buf)) {
+      FIPS202_Reset(ctx);
+      ctx->block_size = block_size;
+      ctx->md_size = bit_len / 8;
+      ctx->pad = pad;
+      return 1;
+    }
+    return 0;
 }
 
+// SHA3 APIs implement SHA3 functionalities on top of FIPS202 API layer
 void SHA3_Reset(KECCAK1600_CTX *ctx) {
   memset(ctx->A, 0, sizeof(ctx->A));
   ctx->buf_load = 0;
   ctx->padded = 0;
 }
 
-int SHA3_Init(KECCAK1600_CTX *ctx, uint8_t pad, size_t bit_len) {
-  size_t block_size;
-
-  // The block size is computed differently depending on which algorithm
-  // is calling |SHA3_Init|:
-  //   - for SHA3 we compute it by calling SHA3_BLOCKSIZE(bit_len)
-  //     because the block size depends on the digest bit-length,
-  //   - for SHAKE we take the block size from the context.
-  // We use the given padding character to differentiate between SHA3 and SHAKE.
-  if (pad == SHA3_PAD_CHAR) {
-    block_size = SHA3_BLOCKSIZE(bit_len);
-  } else if (pad == SHAKE_PAD_CHAR) {
-    block_size = ctx->block_size;
-  } else {
-    return 0;
-  }
-  ctx->padded = 0;
-  
-  if (block_size <= sizeof(ctx->buf)) {
-    SHA3_Reset(ctx);
-    ctx->block_size = block_size;
-    ctx->md_size = bit_len / 8;
-    ctx->pad = pad;
-    return 1;
+int SHA3_Init(KECCAK1600_CTX *ctx, size_t bit_len) {
+  if (bit_len == SHA3_224_DIGEST_BITLENGTH || 
+      bit_len == SHA3_256_DIGEST_BITLENGTH || 
+      bit_len == SHA3_384_DIGEST_BITLENGTH || 
+      bit_len == SHA3_512_DIGEST_BITLENGTH) { 
+        // |block_size| depends on the SHA3 |bit_len| output (digest) length
+        return FIPS202_Init(ctx, SHA3_PAD_CHAR, SHA3_BLOCKSIZE(bit_len), bit_len);
   }
   return 0;
 }
@@ -230,3 +224,19 @@ int SHA3_Final(uint8_t *md, KECCAK1600_CTX *ctx) {
 
   return 1;
 }
+
+// SHAKE APIs implement SHAKE functionalities on top of FIPS202 API layer
+int SHAKE_Init(KECCAK1600_CTX *ctx, size_t block_size) {
+  if (block_size == SHAKE128_BLOCKSIZE ||
+      block_size == SHAKE256_BLOCKSIZE) {
+        // |block_size| depends on the SHAKE security level
+        // The output length |bit_len| is initialized to 0
+        return FIPS202_Init(ctx, SHAKE_PAD_CHAR, block_size, 0);
+  }
+  return 0;
+}
+
+int SHAKE_Final(uint8_t *md, KECCAK1600_CTX *ctx, size_t len) {
+  ctx->md_size = len;
+  return SHA3_Final(md, ctx);
+}
\ No newline at end of file
diff --git a/crypto/fipsmodule/sha/sha3_test.cc b/crypto/fipsmodule/sha/sha3_test.cc
index 23cba17886..9e45ddf7d1 100644
--- a/crypto/fipsmodule/sha/sha3_test.cc
+++ b/crypto/fipsmodule/sha/sha3_test.cc
@@ -208,7 +208,7 @@ TEST(KeccakInternalTest, SqueezeOutputBufferOverflow) {
   const size_t out_lens[] = {
       0, 1, 2, 3, 4, 5, 6, 7, 8, (1 << 5), (1 << 16) + 1};
   for (auto out_len : out_lens) {
-    EXPECT_TRUE(SHA3_Init(&ctx, SHA3_PAD_CHAR, SHA3_384_DIGEST_BITLENGTH));
+    EXPECT_TRUE(SHA3_Init(&ctx, SHA3_384_DIGEST_BITLENGTH));
     out.resize(out_len + canary.size());
     std::copy(canary.begin(), canary.end(), out.end() - canary.size());
     Keccak1600_Squeeze(ctx.A, out.data(), out_len, ctx.block_size, 1);