diff --git a/src/sha256.c b/src/sha256.c
new file mode 100644
index 0000000..2078579
--- /dev/null
+++ b/src/sha256.c
@@ -0,0 +1,214 @@
+/*
+ * Code originally from LibTomCrypt -- Licensed under the Public Domain/WTFPL2.0
+ */
+
+#include "sha256.h"
+#include "sha.h"
+
+/* Various logical functions */
+#define Ch(x, y, z) (z ^ (x & (y ^ z)))
+#define Maj(x, y, z) (((x | y) & z) | (x & y))
+#define S(x, n) RORc((x), (n))
+#define R(x, n) (((x)&0xFFFFFFFFUL) >> (n))
+#define Sigma0(x) (S(x, 2) ^ S(x, 13) ^ S(x, 22))
+#define Sigma1(x) (S(x, 6) ^ S(x, 11) ^ S(x, 25))
+#define Gamma0(x) (S(x, 7) ^ S(x, 18) ^ R(x, 3))
+#define Gamma1(x) (S(x, 17) ^ S(x, 19) ^ R(x, 10))
+
+static void sha256_compress(sha256_context *md, const uint8_t *buf)
+{
+    uint32_t S[8], W[64], t0, t1;
+    int i;
+
+    /* copy state into S */
+    for (i = 0; i < 8; i++) {
+        S[i] = md->state[i];
+    }
+
+    /* copy the state into 512-bits into W[0..15] */
+    for (i = 0; i < 16; i++) {
+        LOAD32H(W[i], buf + (4 * i));
+    }
+
+    /* fill W[16..63] */
+    for (i = 16; i < 64; i++) {
+        W[i] = Gamma1(W[i - 2]) + W[i - 7] + Gamma0(W[i - 15]) + W[i - 16];
+    }
+
+    /* Compress */
+#define RND(a, b, c, d, e, f, g, h, i, ki)        \
+    t0 = h + Sigma1(e) + Ch(e, f, g) + ki + W[i]; \
+    t1 = Sigma0(a) + Maj(a, b, c);                \
+    d += t0;                                      \
+    h = t0 + t1;
+
+    RND(S[0], S[1], S[2], S[3], S[4], S[5], S[6], S[7], 0, 0x428a2f98);
+    RND(S[7], S[0], S[1], S[2], S[3], S[4], S[5], S[6], 1, 0x71374491);
+    RND(S[6], S[7], S[0], S[1], S[2], S[3], S[4], S[5], 2, 0xb5c0fbcf);
+    RND(S[5], S[6], S[7], S[0], S[1], S[2], S[3], S[4], 3, 0xe9b5dba5);
+    RND(S[4], S[5], S[6], S[7], S[0], S[1], S[2], S[3], 4, 0x3956c25b);
+    RND(S[3], S[4], S[5], S[6], S[7], S[0], S[1], S[2], 5, 0x59f111f1);
+    RND(S[2], S[3], S[4], S[5], S[6], S[7], S[0], S[1], 6, 0x923f82a4);
+    RND(S[1], S[2], S[3], S[4], S[5], S[6], S[7], S[0], 7, 0xab1c5ed5);
+    RND(S[0], S[1], S[2], S[3], S[4], S[5], S[6], S[7], 8, 0xd807aa98);
+    RND(S[7], S[0], S[1], S[2], S[3], S[4], S[5], S[6], 9, 0x12835b01);
+    RND(S[6], S[7], S[0], S[1], S[2], S[3], S[4], S[5], 10, 0x243185be);
+    RND(S[5], S[6], S[7], S[0], S[1], S[2], S[3], S[4], 11, 0x550c7dc3);
+    RND(S[4], S[5], S[6], S[7], S[0], S[1], S[2], S[3], 12, 0x72be5d74);
+    RND(S[3], S[4], S[5], S[6], S[7], S[0], S[1], S[2], 13, 0x80deb1fe);
+    RND(S[2], S[3], S[4], S[5], S[6], S[7], S[0], S[1], 14, 0x9bdc06a7);
+    RND(S[1], S[2], S[3], S[4], S[5], S[6], S[7], S[0], 15, 0xc19bf174);
+    RND(S[0], S[1], S[2], S[3], S[4], S[5], S[6], S[7], 16, 0xe49b69c1);
+    RND(S[7], S[0], S[1], S[2], S[3], S[4], S[5], S[6], 17, 0xefbe4786);
+    RND(S[6], S[7], S[0], S[1], S[2], S[3], S[4], S[5], 18, 0x0fc19dc6);
+    RND(S[5], S[6], S[7], S[0], S[1], S[2], S[3], S[4], 19, 0x240ca1cc);
+    RND(S[4], S[5], S[6], S[7], S[0], S[1], S[2], S[3], 20, 0x2de92c6f);
+    RND(S[3], S[4], S[5], S[6], S[7], S[0], S[1], S[2], 21, 0x4a7484aa);
+    RND(S[2], S[3], S[4], S[5], S[6], S[7], S[0], S[1], 22, 0x5cb0a9dc);
+    RND(S[1], S[2], S[3], S[4], S[5], S[6], S[7], S[0], 23, 0x76f988da);
+    RND(S[0], S[1], S[2], S[3], S[4], S[5], S[6], S[7], 24, 0x983e5152);
+    RND(S[7], S[0], S[1], S[2], S[3], S[4], S[5], S[6], 25, 0xa831c66d);
+    RND(S[6], S[7], S[0], S[1], S[2], S[3], S[4], S[5], 26, 0xb00327c8);
+    RND(S[5], S[6], S[7], S[0], S[1], S[2], S[3], S[4], 27, 0xbf597fc7);
+    RND(S[4], S[5], S[6], S[7], S[0], S[1], S[2], S[3], 28, 0xc6e00bf3);
+    RND(S[3], S[4], S[5], S[6], S[7], S[0], S[1], S[2], 29, 0xd5a79147);
+    RND(S[2], S[3], S[4], S[5], S[6], S[7], S[0], S[1], 30, 0x06ca6351);
+    RND(S[1], S[2], S[3], S[4], S[5], S[6], S[7], S[0], 31, 0x14292967);
+    RND(S[0], S[1], S[2], S[3], S[4], S[5], S[6], S[7], 32, 0x27b70a85);
+    RND(S[7], S[0], S[1], S[2], S[3], S[4], S[5], S[6], 33, 0x2e1b2138);
+    RND(S[6], S[7], S[0], S[1], S[2], S[3], S[4], S[5], 34, 0x4d2c6dfc);
+    RND(S[5], S[6], S[7], S[0], S[1], S[2], S[3], S[4], 35, 0x53380d13);
+    RND(S[4], S[5], S[6], S[7], S[0], S[1], S[2], S[3], 36, 0x650a7354);
+    RND(S[3], S[4], S[5], S[6], S[7], S[0], S[1], S[2], 37, 0x766a0abb);
+    RND(S[2], S[3], S[4], S[5], S[6], S[7], S[0], S[1], 38, 0x81c2c92e);
+    RND(S[1], S[2], S[3], S[4], S[5], S[6], S[7], S[0], 39, 0x92722c85);
+    RND(S[0], S[1], S[2], S[3], S[4], S[5], S[6], S[7], 40, 0xa2bfe8a1);
+    RND(S[7], S[0], S[1], S[2], S[3], S[4], S[5], S[6], 41, 0xa81a664b);
+    RND(S[6], S[7], S[0], S[1], S[2], S[3], S[4], S[5], 42, 0xc24b8b70);
+    RND(S[5], S[6], S[7], S[0], S[1], S[2], S[3], S[4], 43, 0xc76c51a3);
+    RND(S[4], S[5], S[6], S[7], S[0], S[1], S[2], S[3], 44, 0xd192e819);
+    RND(S[3], S[4], S[5], S[6], S[7], S[0], S[1], S[2], 45, 0xd6990624);
+    RND(S[2], S[3], S[4], S[5], S[6], S[7], S[0], S[1], 46, 0xf40e3585);
+    RND(S[1], S[2], S[3], S[4], S[5], S[6], S[7], S[0], 47, 0x106aa070);
+    RND(S[0], S[1], S[2], S[3], S[4], S[5], S[6], S[7], 48, 0x19a4c116);
+    RND(S[7], S[0], S[1], S[2], S[3], S[4], S[5], S[6], 49, 0x1e376c08);
+    RND(S[6], S[7], S[0], S[1], S[2], S[3], S[4], S[5], 50, 0x2748774c);
+    RND(S[5], S[6], S[7], S[0], S[1], S[2], S[3], S[4], 51, 0x34b0bcb5);
+    RND(S[4], S[5], S[6], S[7], S[0], S[1], S[2], S[3], 52, 0x391c0cb3);
+    RND(S[3], S[4], S[5], S[6], S[7], S[0], S[1], S[2], 53, 0x4ed8aa4a);
+    RND(S[2], S[3], S[4], S[5], S[6], S[7], S[0], S[1], 54, 0x5b9cca4f);
+    RND(S[1], S[2], S[3], S[4], S[5], S[6], S[7], S[0], 55, 0x682e6ff3);
+    RND(S[0], S[1], S[2], S[3], S[4], S[5], S[6], S[7], 56, 0x748f82ee);
+    RND(S[7], S[0], S[1], S[2], S[3], S[4], S[5], S[6], 57, 0x78a5636f);
+    RND(S[6], S[7], S[0], S[1], S[2], S[3], S[4], S[5], 58, 0x84c87814);
+    RND(S[5], S[6], S[7], S[0], S[1], S[2], S[3], S[4], 59, 0x8cc70208);
+    RND(S[4], S[5], S[6], S[7], S[0], S[1], S[2], S[3], 60, 0x90befffa);
+    RND(S[3], S[4], S[5], S[6], S[7], S[0], S[1], S[2], 61, 0xa4506ceb);
+    RND(S[2], S[3], S[4], S[5], S[6], S[7], S[0], S[1], 62, 0xbef9a3f7);
+    RND(S[1], S[2], S[3], S[4], S[5], S[6], S[7], S[0], 63, 0xc67178f2);
+
+#undef RND
+
+    /* feedback */
+    for (i = 0; i < 8; i++) {
+        md->state[i] = md->state[i] + S[i];
+    }
+    return;
+}
+
+void sha256_init(sha256_context *md)
+{
+    md->curlen = 0;
+    md->length = 0;
+    md->state[0] = 0x6A09E667UL;
+    md->state[1] = 0xBB67AE85UL;
+    md->state[2] = 0x3C6EF372UL;
+    md->state[3] = 0xA54FF53AUL;
+    md->state[4] = 0x510E527FUL;
+    md->state[5] = 0x9B05688CUL;
+    md->state[6] = 0x1F83D9ABUL;
+    md->state[7] = 0x5BE0CD19UL;
+    return;
+}
+
+void sha256_process(sha256_context *md, const uint8_t *in, size_t inlen)
+{
+    size_t n;
+    if (md->curlen > sizeof(md->buf)) {
+        return;
+    }
+    if ((md->length + inlen) < md->length) {
+        return;
+    }
+    while (inlen > 0) {
+        if (md->curlen == 0 && inlen >= 64) {
+            sha256_compress(md, in);
+            md->length += 64 * 8;
+            in += 64;
+            inlen -= 64;
+        } else {
+            n = (((inlen) < ((64 - md->curlen))) ? (inlen)
+                                                 : ((64 - md->curlen)));
+            memcpy(md->buf + md->curlen, in, (size_t)n);
+            md->curlen += n;
+            in += n;
+            inlen -= n;
+            if (md->curlen == 64) {
+                sha256_compress(md, md->buf);
+                md->length += 8 * 64;
+                md->curlen = 0;
+            }
+        }
+    }
+    return;
+}
+
+void sha256_done(sha256_context *md, uint8_t *out)
+{
+    int i;
+
+    if (md->curlen >= sizeof(md->buf)) {
+        return;
+    }
+
+    /* increase the length of the message */
+    md->length += md->curlen * 8;
+
+    /* append the '1' bit */
+    md->buf[md->curlen++] = (unsigned char)0x80;
+
+    /* if the length is currently above 56 bytes we append zeros
+     * then compress.  Then we can fall back to padding zeros and length
+     * encoding like normal.
+     */
+    if (md->curlen > 56) {
+        while (md->curlen < 64) {
+            md->buf[md->curlen++] = (unsigned char)0;
+        }
+        sha256_compress(md, md->buf);
+        md->curlen = 0;
+    }
+
+    /* pad upto 56 bytes of zeroes */
+    while (md->curlen < 56) {
+        md->buf[md->curlen++] = (unsigned char)0;
+    }
+
+    /* store length */
+    STORE64H(md->length, md->buf + 56);
+    sha256_compress(md, md->buf);
+
+    /* copy output */
+    for (i = 0; i < 8; i++) {
+        STORE32H(md->state[i], out + (4 * i));
+    }
+    return;
+}
+
+void sha256_hash(const uint8_t *data, size_t len, uint8_t *digest)
+{
+    sha256_context md;
+    sha256_init(&md);
+    sha256_process(&md, data, len);
+    sha256_done(&md, digest);
+}
diff --git a/src/sha256.h b/src/sha256.h
new file mode 100644
index 0000000..e653e70
--- /dev/null
+++ b/src/sha256.h
@@ -0,0 +1,34 @@
+/* public api for Thomas Pornin's BearSSL SHA-256 implementation */
+
+/** @file
+ *  SHA-256 hash API.
+ */
+
+#ifndef __LIBSTROPHE_SHA256_H__
+#define __LIBSTROPHE_SHA256_H__
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* make sure the stdint.h types are available */
+#include "ostypes.h"
+
+typedef struct {
+    uint64_t length;
+    uint32_t state[8], curlen;
+    uint8_t buf[64];
+} sha256_context;
+
+#define SHA256_DIGEST_SIZE 32
+
+void sha256_init(sha256_context *md);
+void sha256_process(sha256_context *md, const uint8_t *in, size_t inlen);
+void sha256_done(sha256_context *md, uint8_t *out);
+
+void sha256_hash(const uint8_t *data, size_t len, uint8_t *digest);
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __LIBSTROPHE_SHA256_H__ */