diff --git a/packages/circuits/utils/bytes2ints.circom b/packages/circuits/utils/bytes2ints.circom
new file mode 100644
index 000000000..29e7fc5a8
--- /dev/null
+++ b/packages/circuits/utils/bytes2ints.circom
@@ -0,0 +1,41 @@
+
+pragma circom 2.1.5;
+
+include "circomlib/circuits/bitify.circom";
+include "circomlib/circuits/comparators.circom";
+include "circomlib/circuits/poseidon.circom";
+include "./constants.circom";
+
+function compute_ints_size(bytes_size) {
+    var pack_bytes = pack_bytes_const();
+    var remain = bytes_size % pack_bytes;
+    var num_chunk = (bytes_size - remain) / pack_bytes;
+    if(remain>0) {
+        num_chunk += 1;
+    }
+    return num_chunk;
+}
+
+template Bytes2Ints(bytes_size) {
+    var num_chunk = compute_ints_size(bytes_size);
+    signal input bytes[bytes_size];
+    signal output ints[num_chunk];
+
+    var pack_bytes = pack_bytes_const();
+    signal ints_sums[num_chunk][pack_bytes];
+    for(var i=0; i<num_chunk; i++) {
+        for(var j=0; j<pack_bytes; j++) {
+            var idx = pack_bytes*i+j;
+            if(idx>=bytes_size) {
+                ints_sums[i][j] <== ints_sums[i][j-1];
+            } else if (j==0){
+                ints_sums[i][j] <== bytes[idx];
+            } else {
+                ints_sums[i][j] <== ints_sums[i][j-1] + (1<<(8*j)) * bytes[idx];
+            }
+        }
+    }
+    for(var i=0; i<num_chunk; i++) {
+        ints[i] <== ints_sums[i][pack_bytes-1];
+    }
+}
\ No newline at end of file
diff --git a/packages/circuits/utils/constants.circom b/packages/circuits/utils/constants.circom
new file mode 100644
index 000000000..72993280e
--- /dev/null
+++ b/packages/circuits/utils/constants.circom
@@ -0,0 +1,25 @@
+pragma circom 2.1.5;
+
+function email_max_bytes_const() {
+    return 256;
+}
+
+function domain_len_const() {
+    return 255;
+}
+
+function invitation_code_len_const() {
+    return 64;
+}
+
+function field_pack_bits_const() {
+    return 248;
+}
+
+function pack_bytes_const() {
+    return 31;
+}
+
+function timestamp_len_const() {
+    return 10;
+}
diff --git a/packages/circuits/utils/digit2int.circom b/packages/circuits/utils/digit2int.circom
new file mode 100644
index 000000000..f644a71a2
--- /dev/null
+++ b/packages/circuits/utils/digit2int.circom
@@ -0,0 +1,30 @@
+
+pragma circom 2.1.5;
+
+include "circomlib/circuits/bitify.circom";
+include "circomlib/circuits/comparators.circom";
+include "circomlib/circuits/poseidon.circom";
+include "./constants.circom";
+
+
+// `in` is a big-endtian digit string of `out`.
+template Digit2Int(n) {
+    signal input in[n];
+    signal output out;
+
+    component digit2int[n];
+    signal sums[n+1];
+    sums[0] <== 0;
+    for(var i = 0; i < n; i++) {
+        digit2int[i] = Digit2Int1();
+        digit2int[i].in <== in[i];
+        sums[i+1] <== 10 * sums[i] + digit2int[i].out;
+    }
+    out <== sums[n];
+}
+
+template Digit2Int1() {
+    signal input in;
+    signal output out;
+    out <== in - 48;
+}
\ No newline at end of file
diff --git a/packages/circuits/utils/email_addr_commit.circom b/packages/circuits/utils/email_addr_commit.circom
new file mode 100644
index 000000000..98a2a54d7
--- /dev/null
+++ b/packages/circuits/utils/email_addr_commit.circom
@@ -0,0 +1,18 @@
+
+pragma circom 2.1.5;
+
+include "circomlib/circuits/poseidon.circom";
+
+// email_addr_commit = hash(rand, emailAddr||0..0)
+template EmailAddrCommit(num_ints) {
+    signal input rand;
+    signal input email_addr_ints[num_ints];
+    signal output commit;
+
+    component poseidon = Poseidon(1+num_ints);
+    poseidon.inputs[0] <== rand;
+    for(var i=0; i<num_ints; i++) {
+        poseidon.inputs[1+i] <== email_addr_ints[i];
+    }
+    commit <== poseidon.out;
+}
\ No newline at end of file
diff --git a/packages/circuits/utils/email_nullifier.circom b/packages/circuits/utils/email_nullifier.circom
new file mode 100644
index 000000000..e8f2c6c80
--- /dev/null
+++ b/packages/circuits/utils/email_nullifier.circom
@@ -0,0 +1,24 @@
+
+pragma circom 2.1.5;
+
+include "circomlib/circuits/poseidon.circom";
+
+template EmailNullifier() {
+    // signal input header_hash[256];
+    signal input sign_hash;
+
+    signal output email_nullifier;
+
+    // var field_pack_bits = field_pack_bits_const();
+
+    // signal header_hash_int[field_pack_bits+1];
+    // header_hash_int[0] <== 0;
+    // for(var i = 0; i < field_pack_bits; i++) {
+    //     header_hash_int[i+1] <== 2 * header_hash_int[i] + header_hash[i];
+    // }
+    // signal email_nullifier_input[1];
+    // email_nullifier_input[0] <== sign_hash;
+    email_nullifier <== Poseidon(1)([sign_hash]);
+}
+
+
diff --git a/packages/circuits/utils/hash_sign.circom b/packages/circuits/utils/hash_sign.circom
new file mode 100644
index 000000000..62775d1ef
--- /dev/null
+++ b/packages/circuits/utils/hash_sign.circom
@@ -0,0 +1,38 @@
+
+pragma circom 2.1.5;
+
+include "circomlib/circuits/poseidon.circom";
+
+template HashSign(n,k) {
+    // signal input pubkey[k];
+    signal input signature[k];
+
+    // signal output pubkey_hash;
+    signal output sign_hash;    
+
+    var k2_chunked_size = k >> 1;
+    if(k % 2 == 1) {
+        k2_chunked_size += 1;
+    }
+    signal output sign_ints[k2_chunked_size];
+
+    // signal pubkey_hash_input[k2_chunked_size];
+    // for(var i = 0; i < k2_chunked_size; i++) {
+    //     if(i==k2_chunked_size-1 && k2_chunked_size % 2 == 1) {
+    //         pubkey_hash_input[i] <== pubkey[2*i];
+    //     } else {
+    //         pubkey_hash_input[i] <== pubkey[2*i] + (1<<n) * pubkey[2*i+1];
+    //     }
+    // }
+    // pubkey_hash <== Poseidon(k2_chunked_size)(pubkey_hash_input);
+    for(var i = 0; i < k2_chunked_size; i++) {
+        if(i==k2_chunked_size-1 && k2_chunked_size % 2 == 1) {
+            sign_ints[i] <== signature[2*i];
+        } else {
+            sign_ints[i] <== signature[2*i] + (1<<n) * signature[2*i+1];
+        }
+    }
+    sign_hash <== Poseidon(k2_chunked_size)(sign_ints);
+}
+
+
diff --git a/packages/circuits/utils/hex2int.circom b/packages/circuits/utils/hex2int.circom
new file mode 100644
index 000000000..5a264df65
--- /dev/null
+++ b/packages/circuits/utils/hex2int.circom
@@ -0,0 +1,69 @@
+
+pragma circom 2.1.5;
+
+include "circomlib/circuits/bitify.circom";
+include "circomlib/circuits/comparators.circom";
+include "circomlib/circuits/poseidon.circom";
+include "./constants.circom";
+
+// `in` is a big-endtian hex string of `out`.
+template Hex2Field() {
+    signal input in[64];
+    signal output out;
+    signal bytes[32] <== Hex2Ints(64)(in);
+    signal sums[33];
+    sums[0] <== 0;
+    for(var i = 0; i < 32; i++) {
+        sums[i+1] <== 256 * sums[i] + bytes[i];
+    }
+    out <== sums[32];
+}
+
+template Hex2Ints(n) {
+    assert(n % 2 == 0);
+    var bytes = n / 2;
+    signal input in[n];
+    signal output out[bytes];
+
+    component hex2int[n];
+    for(var i = 0; i < bytes; i++) {
+        for(var j = 0; j < 2; j++) {
+            hex2int[2*i+j] = Hex2Int1();
+            hex2int[2*i+j].in <== in[2*i+j];
+        }
+        out[i] <== 16 * hex2int[2*i].out + hex2int[2*i+1].out;  
+    }
+}
+
+template Hex2Int1() {
+    signal input in;
+    signal output out;
+
+    // the given char is [0-9].
+    signal is_digit_min_in[2];
+    is_digit_min_in[0] <== in;
+    is_digit_min_in[1] <== 48;
+    signal is_digit_min <== GreaterEqThan(8)(is_digit_min_in);
+    signal is_digit_max_in[2];
+    is_digit_max_in[0] <== in;
+    is_digit_max_in[1] <== 57;
+    signal is_digit_max <== LessEqThan(8)(is_digit_max_in);
+    signal is_digit <== is_digit_min * is_digit_max;
+    
+    // the given char is [a-f].
+    signal is_alphabet_min_in[2];
+    is_alphabet_min_in[0] <== in;
+    is_alphabet_min_in[1] <== 97;
+    signal is_alphabet_min <== GreaterEqThan(8)(is_alphabet_min_in);
+    signal is_alphabet_max_in[2];
+    is_alphabet_max_in[0] <== in;
+    is_alphabet_max_in[1] <== 102;
+    signal is_alphabet_max <== LessEqThan(8)(is_alphabet_max_in);
+    signal is_alphabet <== is_alphabet_min * is_alphabet_max;
+
+    is_digit + is_alphabet === 1;  
+    signal digit_int <== is_digit * (in - 48);
+    // 87 = 97 - 10
+    signal alphabet_int <== is_alphabet * (in - 87);
+    out <== digit_int + alphabet_int;
+}
\ No newline at end of file